Journal of Mechanical Engineering 2012 6

http://www.sv-jme.eu

58 (2012) 6

Strojniški vestnik Journal of Mechanical Engineering

Since 1955

Papers

367

Zoran Jakšić, Momčilo Milinović, Danijela Randjelović: Nanotechnological Enhancement of Infrared Detectors by Plasmon Resonance in Transparent Conductive Oxide Nanoparticles

376

Branko Livada, Radomir Janković, Nebojša Nikolić: AFV Vetronics: Displays Design Criteria

386

Milenko Andrić, Boban Bondžulić, Bojan Zrnić, Aleksandar Kari, Goran Dikić: Acoustic Experimental Data Analysis of Moving Targets Echoes Observed by Doppler Radars

394

Momčilo Milinović, Damir Jerković, Olivera Jeremić, Mitar Kovač: Experimental and Simulation Testing of Flight Spin Stability for Small Caliber Cannon Projectile

403

Slobodan Jaramaz, Dejan Micković, Predrag Elek, Dragana Jaramaz, Dušan Micković: A Model for Shaped Charge Warhead Design

Martin Macko, Slobodan Ilić, Mirko Jezdimirović: 411 The Influence of Part Dimensions and Tolerance Size to Trigger Characteristics

416

Jure Bernetič, Tomaž Vuherer, Matjaž Marčetič, Mladen Vuruna: Experimental Research on New Grade of Steel Protective Material for the Light Armored Vehicles

422

Hajro Ismar, Zijah Burzic, Nenad J. Kapor, Tugomir Kokelj: Experimental Investigation of High-Strength Structural Steel Welds

Journal of Mechanical Engineering - Strojniški vestnik

Contents

6 year 2012 volume 58 no.

Strojniški vestnik – Journal of Mechanical Engineering (SV-JME) Aim and Scope The international journal publishes original and (mini)review articles covering the concepts of materials science, mechanics, kinematics, thermodynamics, energy and environment, mechatronics and robotics, fluid mechanics, tribology, cybernetics, industrial engineering and structural analysis.

The journal follows new trends and progress proven practice in the mechanical engineering and also in the closely related sciences as are electrical, civil and process engineering, medicine, microbiology, ecology, agriculture, transport systems, aviation, and others, thus creating a unique forum for interdisciplinary or multidisciplinary dialogue.

The international conferences selected papers are welcome for publishing as a special issue of SV-JME with invited co-editor(s).

Editor in Chief Vincenc Butala University of Ljubljana Faculty of Mechanical Engineering, Slovenia Guest Editor Momčilo Milinović University of Belgrade Faculty of Mechanical Engineering, Serbia Technical Editor Pika Škraba University of Ljubljana Faculty of Mechanical Engineering, Slovenia Editorial Office University of Ljubljana (UL) Faculty of Mechanical Engineering SV-JME Aškerčeva 6, SI-1000 Ljubljana, Slovenia Phone: 386-(0)1-4771 137 Fax: 386-(0)1-2518 567 E-mail: info@sv-jme.eu, http://www.sv-jme.eu Print Tiskarna Knjigoveznica Radovljica, printed in 480 copies Founders and Publishers University of Ljubljana (UL) Faculty of Mechanical Engineering, Slovenia University of Maribor (UM) Faculty of Mechanical Engineering, Slovenia Association of Mechanical Engineers of Slovenia

http://www.sv-jme.eu

58 (2012) 6

Chamber of Commerce and Industry of Slovenia Metal Processing Industry Association

Since 1955

Strojniški vestnik Journal of Mechanical Engineering

Cover: FEM simulated time dependent stress field on chassis of 6×6 light armoured vehicle during demanding terrain mission.

an Bondžulić, Bojan Zrnić, Aleksandar Kari, Goran Dikić: tal Data Analysis of Moving Targets Echoes Observed by

omir Janković, Nebojša Nikolić: lays Design Criteria

ilo Milinović, Danijela Randjelović: Enhancement of Infrared Detectors by Plasmon Resonance ductive Oxide Nanoparticles

Dejan Micković, Predrag Elek, Dragana Jaramaz,

Charge Warhead Design

dan Ilić, Mirko Jezdimirović: rt Dimensions and Tolerance Size to Trigger

ž Vuherer, Matjaž Marčetič, Mladen Vuruna: arch on New Grade of Steel Protective Material ed Vehicles

urzic, Nenad J. Kapor, Tugomir Kokelj: tigation of High-Strength Structural Steel Welds

Journal of Mechanical Engineering - Strojniški vestnik

Damir Jerković, Olivera Jeremić, Mitar Kovač: imulation Testing of Flight Spin Stability for Small Caliber

year

no. 6 2012 58

volume

Image courtesy: Chair of Modelling in Engineering Sciences and Medicine, Faculty of Mechanical Engineering, University of Ljubljana

International Editorial Board Koshi Adachi, Graduate School of Engineering,Tohoku University, Japan Bikramjit Basu, Indian Institute of Technology, Kanpur, India Anton Bergant, Litostroj Power, Slovenia Franci Čuš, UM, Faculty of Mech. Engineering, Slovenia Narendra B. Dahotre, University of Tennessee, Knoxville, USA Matija Fajdiga, UL, Faculty of Mech. Engineering, Slovenia Imre Felde, Bay Zoltan Inst. for Mater. Sci. and Techn., Hungary Jože Flašker, UM, Faculty of Mech. Engineering, Slovenia Bernard Franković, Faculty of Engineering Rijeka, Croatia Janez Grum, UL, Faculty of Mech. Engineering, Slovenia Imre Horvath, Delft University of Technology, Netherlands Julius Kaplunov, Brunel University, West London, UK Milan Kljajin, J.J. Strossmayer University of Osijek, Croatia Janez Kopač, UL, Faculty of Mech. Engineering, Slovenia Franc Kosel, UL, Faculty of Mech. Engineering, Slovenia Thomas Lübben, University of Bremen, Germany Janez Možina, UL, Faculty of Mech. Engineering, Slovenia Miroslav Plančak, University of Novi Sad, Serbia Brian Prasad, California Institute of Technology, Pasadena, USA Bernd Sauer, University of Kaiserlautern, Germany Brane Širok, UL, Faculty of Mech. Engineering, Slovenia Leopold Škerget, UM, Faculty of Mech. Engineering, Slovenia George E. Totten, Portland State University, USA Nikos C. Tsourveloudis, Technical University of Crete, Greece Toma Udiljak, University of Zagreb, Croatia Arkady Voloshin, Lehigh University, Bethlehem, USA President of Publishing Council Jože Duhovnik UL, Faculty of Mechanical Engineering, Slovenia General information Strojniški vestnik – Journal of Mechanical Engineering is published in 11 issues per year (July and August is a double issue).

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6 Contents

Contents Strojniški vestnik - Journal of Mechanical Engineering volume 58, (2012), number 6 Ljubljana, June 2012 ISSN 0039-2480 Published monthly

Guest Editorial Special Issue: Toward Interdisciplinary Research in Advanced Technologies Papers Zoran Jakšić, Momčilo Milinović, Danijela Randjelović: Nanotechnological Enhancement of Infrared Detectors by Plasmon Resonance in Transparent Conductive Oxide Nanoparticles Branko Livada, Radomir Janković, Nebojša Nikolić: AFV Vetronics: Displays Design Criteria Milenko Andrić, Boban Bondžulić, Bojan Zrnić, Aleksandar Kari, Goran Dikić: Acoustic Experimental Data Analysis of Moving Targets Echoes Observed by Doppler Radars Momčilo Milinović, Damir Jerković, Olivera Jeremić, Mitar Kovač: Experimental and Simulation Testing of Flight Spin Stability for Small Caliber Cannon Projectile Slobodan Jaramaz, Dejan Micković, Predrag Elek, Dragana Jaramaz, Dušan Micković: A Model for Shaped Charge Warhead Design Martin Macko, Slobodan Ilić, Mirko Jezdimirović: The Influence of Part Dimensions and Tolerance Size to Trigger Characteristics Jure Bernetič, Tomaž Vuherer, Matjaž Marčetič, Mladen Vuruna: Experimental Research on New Grade of Steel Protective Material for the Light Armored Vehicles Hajro Ismar, Zijah Burzic, Nenad J. Kapor, Tugomir Kokelj: Experimental Investigation of HighStrength Structural Steel Welds

365

367 376 386 394 403 411 416 422

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6 Guest Editorial

Guest Editorial Special Issue: Toward Interdisciplinary Research in Advanced Technologies

A comprehensive improvement of product performance is usually a research topic in specialised branches of advanced technology, and is demonstrated through new achievements and results of applied science. This issue of SV-JME will assist in the identification of activity focus in various integrative fields of mechanical engineering in connection with special research topics, aiming to find a balance between the research demands of applied science and the need for new technological achievements. The issue consists of eight articles divided into three thematic units, presenting applied research in the field of mechatronics, special engineering and steel technologies.

The mechatronics unit consists of three papers. The first paper titled Nanotechnological Enhancement of Infrared Detectors by Plasmon Resonance in Transparent Conductive Oxide Nanoparticles deals with the information and communication sensor technology. The paper is a contribution to modern research of new materials in the mechatronics, and discusses the strategies for the selection of nanotechnological parameters in the development of microsensor elements. The increased performance is beneficial to the development of smaller guided projectiles, and the achievements will also be useful for other applications including the light sensors. The topic of second article AFV Vetronics: Displays Design Criteria are special control technologies, integrated into vehicles which operate in extremely demanding conditions. The work provides a review and opens the questions for a discussion about the quality of equipment integrated in these vehicles, which encompasses several different technologies. The next article in the mechatronics unit Acoustic Experimental Data Analysis Of Moving Targets Echoes Observed By Doppler Radars deals with the methodology for discovering and identifying remote objects of human origin. The work presents the research results in the form of a database, freely accessible on the website to users and researchers all around the world.

The second thematic unit presents the results of integrated research in the sub-fields of applied mechanics, more precisely the applications of special engineering topics. The subject of paper Experimental and Simulation Testing of Flight Spin Stability for Small Caliber Cannon Projectile is the integration of rotary motion dynamics during flight and the aerodynamics. The authors’ original contribution is in the association of mathematical simulations and experimental tests for rotating bodies in motion. The paper titled Model for shaped charge warhead design combines special fracture mechanics and the mechanics of gas explosions with experimentally verified software, developed by the authors. The third paper The Influence Of Part Dimensions And Tolerance Size To Trigger Characteristics researches the relations between precision mechanical design and its consequences on the dynamical effects. The work is backed with simulations performed using the authors’ own software. The topic is important for special and precision engineering.

The third group of papers presents the achievements in the research of technological influences on the properties of steel as the basic structural material in mechanical engineering. The papers Experimental Research on New Grade of Steel Protective Material for Light Armored Vehicles and Experimental Investigation of HighStrength Structural Steel Welds discuss the production and applied technology as factors influencing the demands of steel materials and their structural characteristics.

In place of a conclusion, I would like to stress that in a context of intense development research, this issue of SV-JME can be a modest proof that researchers and designers have recognised the significance of better integration and application of scientific results and their technological applications in special fields of engineering. This is also important for a general level of technical development, which must be a topic of discussion and a goal for the future.

Guest Editor, Prof. dr. Momčilo Milinović 365

366

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 367-375 DOI:10.5545/sv-jme.2011.276

Paper received: 2011-12-20, paper accepted: 2012-03-21 © 2012 Journal of Mechanical Engineering. All rights reserved.

Nanotechnological Enhancement of Infrared Detectors by Plasmon Resonance in Transparent Conductive Oxide Nanoparticles Jakšić, Z. – Milinović, M. – Randjelović, D. Zoran Jakšić1,* – Momčilo Milinović2 – Danijela Randjelović1

1 Institute

of Chemistry, Technology and Metallurgy, University of Belgrade, Serbia of Mechanical Engineering, University of Belgrade, Serbia

2 Faculty

We investigated the use of plasmonic nanotechnology to enhance the performance of semiconductor infrared detectors. An increase of quantum efficiency, responsivity and specific detectivity is obtained by applying transparent conductive oxide (TCO) nanoparticles onto the surface of a photodetector. To this purpose we considered uncooled mercury cadmium telluride (HgCdTe) photoconductive detectors fabricated by isothermal vapor phase epitaxy, but the same procedure can be applied to cryogenically cooled devices, including those of photovoltaic type. The main mechanism of enhancement is light concentration ensured through localized plasmon resonance at the TCO nanoparticles and through enhanced scattering, while the desired wavelength range is reached by a further redshifting through the adjustment of nanoparticle properties. The improvement can be implemented during the final stages of production of the existing photovoltaic and photoconductive detectors. The method is applicable to various practical applications, including updating of high-precision guided ammunition.

Keywords: nanotechnology, homing head, infrared detectors, plasmonic enhancement, transparent metal oxides, nanoparticles

0 INTRODUCTION The possibility of detecting and recognizing objects under low light conditions [1] has applications in many fields, from personal and instrumental surveillance to homing devices utilizing heat seeking guidance. Advanced technological solutions for missile guidance provided in the past have later spread not only to missiles but also to classic projectiles like mortar shells, gun shells, etc., thus forming the basis for “smart ammunition”.

Single-shot lethality is becoming the most important quality requirement for both missiles and guided projectiles. New mortar shells technology [2] and [3], developed in the form of missiles with homing heads, usually depends either on laser illumination of the target for its guidance or an autonomous selfguided heat-seeking mode, as in the case of terminal infrared homing. When using terminal guidance for projectiles the main goal is to develop the recognition of signals reflected from illuminated targets, to hit and kill, to a level of a reliable technical characteristic in the required chain.

This is especially important for fighting any type of combat armored targets in motion, which requires target tracking by laser designator during the projectile terminal approaching phase.

The sensor on the homing head of a guided projectile requires highly sensitive optical detection to recognize reflected laser signals from the target illuminated by a designator and to provide an appropriate signal for the flight control correction of the missile or projectile. The control of the missile or the projectile at the last phase of ballistic trajectory

at distances less than 1000 m requires fast influence on the changes of the missile’s axes or velocity vector direction toward the mobile target. For this type of control [3] the element with the largest influence on the missile shooting performances is the type of detector in the homing head, which has to be sufficiently sensitive to measure the flux and the direction of the light impulse reflected from the illuminated target. The whole process is extremely rapid and the reaction of the homing head and the missile control mechanism directly influence target shooting errors. Since artillery projectiles [3] must be low-cost, compact, rugged and simple, this means that the implementation of the detection function must be performed without additional complex equipment for improving the sensitivity of light flux detection in the homing head sensor. Self-guidance homing heads operate without illumination sources and use infrared (IR) signature of targets to recognize the guidance LOS (line of sight) direction. This means that high response speed and high sensor sensitivity under poor lighting condition and at infrared wavelengths where, typically, the influence of noise and interference is much larger than in visible and further increases with wavelength, must be ensured.

It is well known that semiconductor infrared detectors typically ensure the highest response speed of all detector types [1] and [4]. They do not depend on thermal diffusion at all, contrary to the thermal detectors, but are excited directly by infrared radiation from the target through interband transitions of charge carriers. Such direct conversion from light to electric signal ensures rapid reaction and because of that such detectors are the devices of choice in military systems.

*Corr. Author’s Address: Institute of Chemistry, Technology and Metallurgy, Njegoševa 12, 11000 Belgrade, Serbia, jaksa@nanosys.ihtm.bg.ac.rs

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 367-375

Another issue is how to improve the sensitivity (responsivity) and specific detectivity of infrared detector without simultaneously increasing the system complexity and cost. To this purpose one has to ensure a maximization of light flux within the active area of the detector. This belongs to the field of light management, which is one of the most significant issues with photodetectors generally, regardless of the wavelength range. It is of especial importance for the new homing heads utilizing either laser-illuminated or self-guided missiles and projectiles technology [2] and [3].

The aim of this paper is to present a possible nanotechnological solution for highly sensitive and low-cost infrared semiconductor detectors applicable for various purposes, including updating high-precision guided ammunition. To this purpose, mercury cadmium telluride uncooled photoconductive detectors fabricated by vapor phase epitaxy were considered. Aluminum-doped zinc oxide and tin oxide nanoparticles fabricated by nonaqueous procedure were considered for the improvement of detector samples. The original research results also include the assessment of the optimization wavelength range through redshifting of nanoparticle optical properties.

1 REQUIREMENTS AND CONSTRAINTS FOR INFRARED DETECTORS Active infrared systems, including those for homing heads, utilize as their main principle the detection of infrared radiation, usually at wavelengths belonging to the (3 to 5) mm or (8 to 14) mm atmospheric win­ dows. The infrared photodetec­tors typically used for these ranges are either silicon thermal devices like bolometers, thermocouples, etc. (low-end and slower, but less expensive), or semiconductor detectors utilizing narrow-bandgap materials like indium antimonide or mercury cadmium telluride (much higher performance, a typical choice for military applications). Semiconductor devices offer much higher speeds, high specific detectivities with background-limited infrared photodetector (BLIP) operation and sharply defined operating wavelength ranges. Our present analysis is dedicated to this type of detectors.

Mercury cadmium telluride (Hg1-xCdxTe, MCT) has been the infrared semiconductor material of choice for the last few decades [4]. The possibility to tailor its cadmium molar fraction x during fabrication and thus to design a desired cutoff wavelength makes it useful for various detection ranges, from near to far infrared. The most sensitive Hg1-xCdxTe infrared 368

detectors are the cryogenically cooled ones [1], typically by liquid nitrogen or possibly by multi-stage thermoelectric coolers. However, there is also a class of Hg1-xCdxTe infrared photodetectors that operate at room temperature, furnishing specific detectivities in excess of 108 cmHz1/2/W [5]. Fabrication of these Hg1-xCdxTe infrared photodetectors using isothermal vapor phase epitaxy (ISOVPE) is presented in [6] and by liquid phase epitaxy (LPE) in [7].

It is well known that the performance of an infrared detector is described by its sensitivity and specific detectivity [1]. Sensitivity (also denoted as responsi­vity) is defined as a ratio of the incident infrared flux and the useful signal, which may be either voltage or current. The specific detectivity is further defined as the product of sensitivity and the squared active area divided by detector noise equivalent power. All of the exploitation demands quoted in the Introduction practically require the maximiza­ ti­on of the specific detectivity in order to ensure the photodetector operation under weak illumination condition. On the other hand, this signifies there is a necessity to trap the maximum amount of the useful signal within the active region of the pho­todetector in order to optimize sensitivity (light management within the detector). This con­dition is especially important if the detector active areas are thin, as is usually the case with both ISOVPE and LPE epitaxial layers, but also for other devices from different materials and for other wavelength ranges, including e.g. ultrathin-film solar cells.

Various strategies have been developed to improve the light concentration within the photodetector, including the use of immersion lenses, antireflection coatings and structures, surface reliefs, highly reflective detector back sides, etc. [8].

Among the most recently proposed methods to improve the light flux within the photodetectors is the use of plasmon resonance [9]. Under certain conditions, an interface between dielectric and a material with negative relative dielectric permittivity (for instance good metals like silver or gold) will maintain electromagnetic waves confined to the interface and evanescent (i.e. exponentially decaying) in both directions from the interface surface. Such waves are termed surface plasmons polaritons (SPP).

Plasmon waves may propagate along a planar guide, or be localized e.g. on the surface of nanoparticles (localized SPP). In each of these situations they ensure extremely large concentrations of electromagnetic field. Owing to this, they are very convenient for the enhancement of the operation of photodetectors generally, if the region of the concentrated field

Jakšić, Z. – Milinović, M. – Randjelović, D.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 367-375

2 TECHNOLOGICAL MECHANISM OF LIGHT TRAPPING USING PLASMONIC NANOPARTICLES In this section, we briefly outline the possibility to enhance the quantum efficiency (the number of photocarriers generated by a single incident photon) and specific detectivity of a photodetector (regardless of its wavelength range) when there is only a micrometer-thin active area. To this purpose

we consider a typical composition profile of an Hg1-xCdxTe photodetec­tor, as defined by its cadmium molar fraction x. An experimental dependence of x on the distance from the detector surface is shown in Fig. 1a. The profile was experimentally determined from an ISOVPE-produced detector by IR transmission measurement because the cut-off wavelength of an MCT detector is defined by the lowest value of x, which is the one near the detector surface (left part of Fig. 1a). In several successive steps a submicrometerthin layer was removed from the detector surface utilizing chemical etching and for each thus obtained remaining structure its cut-off was again determined

by IR transmission measurement, while the thickness of the remaining structure was measured utilizing a profilometer.

1.00

Cd molar fraction x

0.75

0.50

0.25

0.00

a)

0

5

10

20

800

Position, mm

Normalized electromagnetic field

coincides with the active region of the photodetector.

Obviously, this is especially useful for very thin detectors. Some methods for plasmonic enhancement that could be further modified for military grade detectors of reflected laser beam were originally proposed for photovoltaic solar cells [10] to [13].

The main problem with the use of plasmonic enhancement for infrared detector is that plasma resonance frequency at which the evanescent wave reaches its peak for metals is in the ultraviolet or visible part of the spectrum [14]. Thus, it is necessary to redshift the plasma frequency towards longer operating wavelengths. Several strategies were proposed to overcome this. One of them is to form complex patterns on detector surface which may serve as nanoaperture arrays [15] and [16] and which support the existence of the so-called designer (“spoof”) plasmons [17]. In this way, the operating wavelength can be tailored to be proportional to the aperture dimensions and the spacing between them. Wavelengths 7 to 8 mm were obtained in this manner [16]. Another redshifting strategy was to immerse metal nanoparticles into a higher refractive index material, which resulted in shifting the characteristics from the visible part of the spectrum to the wavelengths of up to 1.5 mm [9]. Nanoparticles with sandwich structures were also utilized [16] where e.g. non-plasmonic material is covered by a thin shell of plasmonic material or there are several alternating layers of plasmonic and dielectric materials. Finally, one may use alternative low-loss plasmonic materials with intrinsically redshifted plasma frequency, like those described in [18].

In this work we consider possible novel strategies to further improve infrared detection in semiconductor detectors utilizing plasmonics. We consider the replacement of metal nanoparticles by transparent conductive oxides like tin oxide, indium oxide and zinc oxide. We also investigate the possibility to combine these materials with higher-index surrounding dielectric media and with additional patterning to obtain plasmonic scatterers enhancing the performance of thin-film infrared detectors.

b)

4

3

2

1

0

5

10

15

Position, mm

Fig. 1. a) measured Cd molar fraction profile of an MCT layer fabricated by open tube isothermal vapor phase epitaxy at a CdTe substrate; maximum detector response corresponds to the lowest Cd molar fraction, b) intensity of localized evanescent field near the detector surface in the case when a plasmonic layer is deposited on the surface; maximum detector response overlaps with maximum field enhancement

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Since the procedure of epitaxial growth allows the value of x to be tuned in the whole range 0 to 1, it is possible to easily tailor the detector response to a desired detector wavelength range and operating temperature. For instance, the optimum specific detectivity at room temperature and for a 10.6 mm wavelength is obtained for a cadmium molar fraction x = 0.165, while at 77 K and for the same wavelength the value should be x = 0.20.

It can be seen that the thickness of the low-x part is very small, its typical value being 5 to 15 mm. Thus, it is of interest to locate most of the incident optical signal within this part in order to maximize useful absorption. This is where plasmonic enhancement steps in. The plasmonic field is the largest at the surface and exponentially decreases towards the depth of semiconductor. The penetration depth depends on the thickness of the plasmonic material film at the surface and is larger for thinner plasmonic layers.

Such structures are very convenient since the photodetector for a given temperature and wavelength range can be customized by simply tailoring the cadmium molar fraction x. The optical field should be concentrated within the first several micrometers of their active area, and SPP fields suit that purpose well.

Fig. 2a shows the manner in which plasmonic nanoparticles can be utilized to enhance the field in the desired part. Each nanoparticle serves as a scatterer, and its plasmonic characteristics help direct most of the incident light into the active area. In addition to that, the above mentioned enhancement of the field around nanoparticles helps keep most of the light trapped within the near-surface part of the detector volume.

The localized electromagnetic field distribution around a nanoparticle is also shown in Fig. 2 for different situations. This is a qualitative presentation only and does not reflect the exact spatial distribution of the field. In all situations the external electromagnetic wave arrives from top. Fig. 2b shows the simplest case when the nanoparticle (black dot in the middle) is embedded in homogeneous medium. The distribution of the field (shaded grey circle) is symmetrical in forward and backward directions and is decreasing exponentially away from the nanoparticle (higher field is shown by lighter shading). Fig. 2c shows the field distribution when the nanoparticle is at an interface between media 1 and 2, where the refractive index of the bottom medium (2) is larger – the field is preferentially scattered towards the larger index medium. Fig. 2d again shows the electromagnetic field distribution for a nanoparticle at an interface, but this time the refractive index of the 370

top medium (1) is larger. Thus, the incident wave is always “folded” or “trapped” into a thin layer around the nanoparticle.

Fig. 2. Light trapping utilizing plasmonic nanoparticles; a) nanoparticles stochastically placed on the detector surface; b) field localization for a nanoparticle embedded in homogeneous medium (black dot in the centre: nanoparticle; gray circle: enhanced field, darker region corresponding to lower field); c) field localization for a nanoparticle at an interface between lower (1) and higher (2) refractive index medium; d) field localization if higher index medium is (1) and lower (2) AR/dielectric Active layer (MCT) passive semiconductor (CdTe) a)

substrate

b)

c)

diffractive patern d) plasmonic nanoparticless

e)

f)

Fig. 3. Plasmonic structures for light concentration; a) nanoparticles on top of dielectric layer; b) nanoparticles embedded in dielectric; c) nanoparticles on top of active area (case shown in Fig. 1); d) nanoparticles on back side; e) diffractive pattern on top of active area; f) back-side diffractive pattern

Fig. 3 shows some possible geometries to achieve this. Nanoparticles may be placed on the surface

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dielectric layer (antireflection coating, AR), within that coating, or directly on the active surface (the case shown in Figs. 3a to c). In the cases Figs. 3a and c light trapping is represented by Fig. 2c, and in the case 3b by Fig. 2b. Nanoparticles may also be positioned on the detector back side, Fig. 3d. An alternative approach, depicted in Fig. 3e and f is the use of regular patterns which include diffractive gratings, but also subwavelength nanoaperture arrays with extraor­ dinary optical transmission. Such regular patterns may be located at the detector surface (Fig. 3e), or at its back side (Fig. 3f). The trapping in the situations 3d, e, and f is represented by Fig. 2d, since the detector active area has a higher value of refractive index.

3 ENHANCING INFRARED DETECTOR PERFORMANCE USING TRANSPARENT CONDUCTIVE OXIDES Transparent conductive oxides (TCO) are plasmonic materials with their plasma frequency in infrared (compared to good metals where plasma frequency is in ultraviolet). Their relative dielectric permittivity is negative near plasma frequency, and its dispersion is well-described by electron resonance models of Drude or Lorentz [19] to [21]. The Drude model taking into account absorptive losses is:

ε = ε∞ −

ω p2 ω (ω + iΓ )

,

(1)

where ωp is the plasma frequency, Γ denotes damping factor describing losses (i.e. defines the imaginary part of the complex dielectric permittivity), while ε∞ is the asymptotic relative dielectric permittivity.

The plasma frequency is determined by the properties of free carriers in material as:

ω p2 =

ne 2 , m*ε 0

(2)

where n is electron concentration, e is the free electron charge (1.6·10–19 C), ε0 is the free space (vacuum) permittivity (8.854·10–12 F/m), and m* is the electron effective mass.

The damping factor can be calculated from the material scattering data as:

Γ =

e , µ m*

(3)

where μ is mobility of free carriers in TCO. The scattering cross-section of a particle is greatly enhanced by plasma resonance and may reach

values up to 10 times larger than the geometrical cross-section. This means that a surface coverage of about 10% should be sufficient to capture practically 100% of the incident light and convert it into surface plasmons polaritons. The scattering cross-section for plasmonic nanoparticles at a wavelength l can be calculated utilizing the quasi-static approximation as [22]: 4

Cscat =

8 2 π  α   , 3π λ 

(4)

where a is polarizability, with a functional form identical to that of the Clausius-Mossotti relation [23]: ε np −1 ε (5)

α = 3V d . ε np +2 εd Here εnp is the complex and wavelengthdispersive relati­ve dielectric permittivity of the plasmonic nanoparticles, defined by Eq. (1), εd is the permittivity of the surrounding dielectric medium and V is the geometrical volume of the nanoparticle. The plasmon resonance and the maximum scattering crosssection are achieved at εnp = –2·εd. The absorption cross-section is determined as:

Cabs =

2π Im (α ) . λ

(6)

It is important to note that losses within TCO nanoparticles are smaller than those in metals. At the same time, the plasmon resonance wavelength in such nanoparticles is shifted into the infrared part of the spectrum. The particular value of the resonant wavelength can be tailored by doping of TCO. Both facts are very important for the enhancement of the performance of the infrared semiconductor detectors 4 REDSHIFTING STRATEGIES FOR TCO NANOPARTICLES In this section the properties of some possible photodetector enhancement configurations utilizing transparent conductive oxide nanoparticles or full oxide layers are assessed. A situation where plasmonic nanoparticles are deposited directly to the surface of the detector, i.e. the configuration shown in Fig. 2c is considered. An additional antireflection coating can be located over the plasmonic layer.

We analyzed two different TCO nanoparticle materials, tin oxide (TO) and aluminum-doped zinc oxide (AZO). The TO nanoparticles are fabricated

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90 120

60

transmitted 30

150

reflected Beam incidence

180

0

Nanoparticle 210

330

TIR sidelobe Critical angle 240

n = 1.8

300 270

Air, n = 1

Fig. 4. Angular distribution of radiation scattered from an AZO nanoparticle located at an interface between air (refractive index n = 1) and a substrate with n = 1.8

Based on the measured and calculated optical and plasmonic properties of these nanoparticles, we performed numerical simulati­on of the IR radiation scattering on them. In accordance with the experimental data quoted in [24] to [26] we considered a spherical dipole TCO nanoparticle with a radius 35 nm, located at an interface between a semi-infinite medium with a refractive index value n = 1 and a layer with n = 1.8. In our simulation the beam was assumed to arrive perpendicularly to the detector surface at a wavelength of 1.4 mm (near infrared). For our calculation we utilized Eqs. (3) to (8) and applied the approach to scattering cross section determination as outlined in [27]. Fig. 4 shows a large enhancement of scattering cross section, together with preferential distribution of the incident power into the photodetector in the direction of the incident beam and with an appearance of sidelobes in the simulated distribution due to the total internal reflection (TIR) effect. Thus, plasmonic nanoparticles made from alternative redshifted materials can be used for the enhancement of photodetector operation 372

in the infrared wavelength range. The presented case corresponds to the situation shown in Fig. 3a, and the active region is located on the left from the nanoparticle. It should be emphasized here that the radial distribution shown in Fig. 4 is related with a single plasmonic nanoparticle only (its dimensions and properties being defined above) and does not directly reflect the overall photodetector element performance which is further defined by the specific detectivity enhancement.

A further redshifting strategy for plasmonic nanoparticles is to embed them into a medium with a value of refractive index higher than that of the nanoparticle [28]. The influence of the embedding medium with a higher value of dielectric permittivity was numerically assessed utilizing a simplified scattering model from [29]. The dielectric permittivity of the nanoparticle was determined using the simple mixing model, (εtotal = [εparticle + εmedium]/2).

The normalized cross-section is defined here in the usual manner as the ratio of the power scattered by a particle versus the total power intercepted by it. The simulated results shown in Fig. 5 show that an increase of the dielectric permittivity of the surrounding medium shifts the cross-section maximum towards longer infrared wavelengths. A very similar effect had previously been reported for metal plasmonic nanoparticles at shorter wavelengths [28].

Normalized scattering cross-section

utilizing a non-aqueous approach in autoclaves starting from a simple solution of SnCl4 in benzyl alcohol, while AZO is produced in pressurized reaction vessels in a microwave system. The nanoparticles size and morphology were characterized by scanning electron microscopy (SEM). Details on the fabrication and characterization procedures of these materials are out of the scope of this paper and can be found in [24] to [26].

1.0

0.8

ε=1

ε=2

ε=3

ε=4

0.6

0.4

0.2

0.0 800 1000

1400

1800

2200 2500

Wavelength, nm

Fig. 5. Assessment of the influence of embedding medium permittivity (shown in figure for each corresponding curve) to the scattering cross-section of TCO nanoparticles; for easier comparison, all peaks are normalized to the same value

Another method to tailor the position of the scattering cross-section peak is to influence the density of nanoparticles, i.e. to change the distance between them, as proposed in [30], where the authors considered silica nanospheres with gold shell, i.e. hollow plasmonic nanoparticles. The influence of the distance between separate nanoparticles to the

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redshifting of the normalized scattering cross-section peak was assessed, as shown in Fig. 6. It can be seen that a decrease of the distance between nanoparticles causes a shift of the peak toward longer wavelengths.

A detailed account on the redshifting due to the interaction of closely adjacent nanoparticles based on finite element modeling can be found in [31].

Normalized scattering cross-section

1.0 30 nm

3 nm

0.9 nm

0.8

0.6

0.4

0.2

0.0 800

1000

1200

1400

1600

1800

2000

2200

2400

Wavelength, nm tle

Fig. 6. Assessment of the influence of interparticle distance (shown in figure for each corresponding curve) to the scattering cross-section of TCO nanoparticles; for easier comparison, all peaks are normalized to the same value

An important point is how to physically implement the proposed plasmonic enhancement to the existing types of IR HgCdTe detectors. This question reduces to the technology of surface functionalization utilizing thin layers of dispersed nanoparticles [32]. One of the convenient methods to deposit nanoparticles to the existing detector surface is drop coating, where a dispersion of nanoparticles in an inorganic liquid also containing some kind of surfactant agent is utilized.

Our as-produced experimental TCO nanoparticles are already dispersed in benzyl alcohol [24], thus facilitating the procedure. The deposition itself is done using a capillary syringe ensuring accurate control of the deposited amount. After the deposition, the mixture is left to settle, allowing nanoparticles to self-assemble on the photodetector surface. TCO may be deposited in the described manner directly onto the active surface or onto the surface passivation/ antireflection coating. An important point here is that in the latter case the dielectric or heterostructural passivation layer obviously must be much thinner than the localized evanescent field depth.

Regarding the achievable improvements of the photodetector figures of merit, it should be born in mind that light trapping through plasmonic enhancement effectively increases the photodetector optical thickness αd (where α is the absorption coefficient and d the physical thickness of the photodetector). Due

to this reason, the best performance enhancement is expected for very thin detector structures. According to [9], plasmonic light trapping ensures 10- to 100-fold shrinkage of the active region thickness while keeping αd constant. In the first experiments with plasmonic enhancement of photovoltaic photodetectors an approximately 20-fold increase of the photocurrent was observed. The assessment of realistic uncooled HgCdTe photoconductors gives a specific detectivity improvement of about 2 to 2.5, which is strongly dependent on the actual thickness of the lowest Cd molar fraction part of the epitaxial layer.

An advantage of our proposed strategy to utilize alternative plasmonic material like TCO and apply the described redshifting approaches is that transparent conductive oxides inherently have lower losses than the standard plasmonic materials like gold, silver, etc. Thus, we are able to place our nanoparticles at the front surface of the detector (the geometry shown in Fig. 2c) and at the same time to avoid excessive parasitic absorption losses. This is in contrast to metal nanoparticles to be placed near the back side of the detector (which is at the same time technologically more demanding). Also, according to [9], in the case of nanoparticles at the front surface, light will first acquire an angular spread within the active region and thus enhance absorption to subsequently reflect from the detector back side, returning again to the front nanoparticles and thus ensuring re-radiation via the identical scattering mechanism, consequently furnishing an even higher efficiency. Thus, the use of TCO may give us an additional degree of freedom when designing photodetectors and permits us to avoid unnecessary technological changes in the production cycle of photodetector chips, which contributes to simplicity and cost effectiveness.

5 CONCLUSION We analyzed the possibility to enhance the specific detectivity of narrow-bandgap IR detectors utilizing plasmonic nanoparticles. To this purpose, we considered redshifting the absorptance maximum of the nanoparticles utilizing alternative plasmonic materials belonging to the class of transparent conductive oxides, the immersion of such nanoparticles into higher refractive index medium and the adjustment and tailoring of the packaging density of nanoparticles. In all cases the nanoparticles are stochastically distributed directly on the photodetector surface. An advantage is that TCO plasmonic nanoparticles may simultaneously serve as scatterers to enhance the capture of the incident radiation

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and as subwavelength optical “antennas” directly increasing absorption in the photodetector active area through field concentration caused by the presence of evanescent plasmon modes. The redshifting of the signal can help achieve operating wavelengths reaching the mid-infrared range. A further patterning and the application of designer plasmon using regular subwavelength patterns may ensure shifting to the far-infrared part of the spectrum. In this manner, thin film-based uncooled IR detectors could become a viable alternative for different applications, even the high-end ones like the use in homing devices for smart ammunition.

6 ACKNOWLEDGMENT The research presented in this paper was funded by the Ministry of Education and Science of the Republic of Serbia within the projects TR 32008 and III 47029.

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 376-385 DOI:10.5545/sv-jme.2011.279

Paper received: 2011-12-20, paper accepted: 2012-05-18 © 2012 Journal of Mechanical Engineering. All rights reserved.

AFV Vetronics: Displays Design Criteria Livada, B. – Janković, R. – Nikolić, N. Branko Livada1 – Radomir Janković2 – Nebojša Nikolić3 1 Luxell Technologies Ltd., Canada 2 Union University School of Computing, Serbia 3Strategic Research Institute, Serbia

This paper addresses the basic functionalities and properties of displays aimed to be used in modern armoured fighting vehicles (AFV). The paper also establishes a basis to determine the opportunities for a different technology application in the harsh AFV environment. The AFV displays are specified by active area, footprint size and other characteristics such as luminance, resolution, viewing envelope, colour, grey scale, night vision compatibility, and sun light readability. Also, some specific requirements for AFV display properties related to AFV application environment are discussed. This paper further provides a short overview of the key technologies used in display design and their compliance with basic AFV requirements. After ruggedisation of the Commercial Off The Shelf - COTS AMLCD flat panels have been successfully applied, they obtained dominant application in AFV displays. It seems that AMLCD display application in AFV will dominate during this decade.

Keywords: vetronics, AFV displays, Ruggedised displays, AMLCD technology, flat panel displays

0 INTRODUCTION Recent improvements in information and armoured fighting vehicles (AFV) technologies have introduced new directions in development of electronic devices for vehicle control and a new tactical approach for the use of AFVs in battlefields.

Vetronics (Vehicle electronics) is becoming a key feature of both new AFV developments and upgrades of existing vehicles. In general, the architecture of the vetronics system includes some of functional subsystems: • fire control system, • vehicle control, • active suspension, • engine control and monitoring, • sensors control and signal distribution, • data collection and distribution systems, • communication systems.

AFV upgrade projects could use all or only some of the sub-systems listed.

The brisk development of information technology has changed the way warfare is conducted, which is expressed in the so called Network Centric Warfare (NWC) doctrine [1] and [2] and swarming [3] and [4] as a new tactical approach.

In spite of almost 100 years of their deployment in active service, AFV still are one among the most important resources of every contemporary army’s ground forces. Contemporary warfare has significantly changed the way of armed forces use, resulting in the need for research and introduction of new tactical procedures, wherein swarming is the most promising one. In the military sense of the word, swarming [3] is “… a systematic pulsing of force and/ 376

or by dispersed networked units, so as to strike from all directions simultaneously.” An example of AFV swarming tactics is depicted in Fig. 1

Fig. 1. AFV swarming tactics

In order to enable AFVs (main battle tanks, APCs, scout vehicles etc.) acting as swarmers, it is necessary to develop an appropriate C4ISR system [4] and [5] centred on computers, navigation and displays for crew interaction.

The display is one of the key components of C4ISR system, being an integrated piece of equipment for AFV crew access to all information necessary to control motion and actions of their AFV. It enables them to take part in common actions of all AFVs applying swarming tactics: controlled motion and actions within the swarm, and active participation in C4ISR system, both as the information source and recipient.

This paper discusses various display technologies, and how their capabilities could be used in AFV vetronics and AFV Crew Station design. *Corr. Author’s Address: Luxell Technologies Ltd., Mississauga, Canada, blivada@luxell.com

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 376-385

1 AFV VETRONICS SYSTEM STRUCTURE AND REQUIREMENTS AFV vetronics system architectures are still under development [10] to [13]. The key activities are in the field of interface developments and related software developments. Some development results are already applied in new and upgraded AFV projects.

A generalized AFV vetronics system is illustrated in Fig. 2. AFV vetronics architecture tends to integrate vehicle power, physical properties, control software, data transfer and human factors.

ISD – individual sensor displays.

MFD are usually applied at commander and/or Gunner Control Station. VD and HUMS are usually applied at driver and commander control station.

ISD could be applied at drivers control station, and anywhere needed.

A block diagram of typical AVF crew station is depicted in Fig. 3.

•

Fig. 3. AFV crew station block diagram

2 RUGGEDISED DISPLAY STRUCTURE Fig. 2. AFV vetronics generalized architecture

AFVs operate in extreme climatic conditions, and generate harsh mechanical influences. Climatic environmental conditions are usually analyzed and related design requirements are defined using STANAG 2895 [6]. Environmental compliance is usually verified by using MIL STD 810 [7].

Modern AFV displays typically provide the following: • function keys – providing customization of the displayed information, • text and graphic overlay allowing customized HMI (Human Machine Interface) for individual application (reticules, icons, menus etc.), • picture in picture presentation, • connectivity (CANbus, MilCAN, serial RS232, RS422, USB, wireless); • video (analogue NTSC, CCIR RS170, and/or digital DVI), • recording - to be applied as per specific operations and training purposes.

Bearing in mind these requirements, the display workload can be divided into various categories: • MFD – multi-functional displays, • VD – video displays, • MMD – moving map displays, • HUMS – health & usage monitoring station,

Whenever there is a need to obtain some additional display feature for specific application (wide temperature range & harsh environmental influences, high reliability and long lifetime, high ambient illumination readability, etc.) one should ask for a ruggedised display solution [14]. Depending on the application, different levels of ruggedisation and appropriate technical solutions can be applied [15].

Fig. 4. AFV ruggedised display structure

In the present time, preferred solutions use COTS (Commercial off the Shelf) AMLCD panels ruggedised to work properly for specific applications [9]. That adaptation process and/or ruggedisation usually involve the following engineering solutions and changes: Mechanical design: contributes to the display protection from all the specified environmental conditions (temperature, vibration etc.), display

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mechanical interface to the user’s system, and integrate all other design requirements to provide a suitable and compact mechanical design.

Fig. 5. AFV display cover glass structure

Electrical/Hardware design: provides electrical power interface design (external and internal), EMI/ EMC compatibility, AMLCD driving and control circuits, LED backlight driving circuits, backlight control functions, colour sensor and bezel illumination sensor (which are usual in avionics but also possible to be effective in AFV vetronics), temperature sensor, etc.

Software (firmware) design: involves custom design creations leading to an extended range of the display microprocessor controlled functions, required video signal interface and transformation functions, Built-in Test functions (BIT), etc.

Optical design: usually involves design solutions to include a more reliable, high output, wide dimming range LED backlight, and special display optical features such as: NVIS compatibility, high ambient illumination readability, high brightness, high contrast under illumination, etc. Important part of optical design is COTS AMLCD panel selection. All engineering solutions are trade-offs.

As depicted in Fig. 4, a ruggedised display is a complex optoelectronic system, which requires a complex design process joining various technological solutions into unique equipment. The display key subsystems are described below.

Bezel: incorporates switches, pushbuttons and indicators which can be equipped with appropriate backlight including NVIS filtered backlight. Also, ambient light sensors could be used as a part of the display brightness automatic control electronics, as a possibility required by customers.

Housing, mechanical interface: used to provide display parts integration and proper mechanical mounting in the user’s system.

Ruggedised display device: is the display system’s most important part. It integrates the 378

display panel and other technologies into a unique functionality. Generally speaking this part consists of: • touch panel (if required), • front (cover) glass (Fig. 5), providing vandal protection, anti-reflective front surface (if a touch screen is not used), transparent conductive EMI layer, spectral filtering for contrast enhancement and/or NVIS, could be also as the mesh solution to provide better screening, • display device (CRT, FEL, AMLCD, OLED) electronically controlled pixelated structure, • display device heater (for the LCD option), providing low temperature operation.

Backlight: is another critical subsystem (if used) consisting of two main parts: a. optical stack (light collection and beam shaping optics, with possible including of DBEF film for efficiency improving) and b. illumination source (suitable light source, CCFL, White LEDs, RGB LEDs).

The backlight could be designed as: • bottom - direct illuminated (illumination source is distributed inside light integration chamber bellow AMCLD active surface), • side illuminated (illumination source is suited on the side and light is transferred to the AMLCD using waveguide optics).

Backlight driving electronics: energy efficient driving circuits including dimming control electronics, of wide range.

Display driving electronics: drives display pixels (light valves) according to video signal content, as the integral part of LCD cell externally controlled.

Motherboard & microcontroller: integrates all electronics and control circuits.

Software and firmware: application tailored embedded software and firmware controlling display functions and controls.

Communication interface electronics electronic boards designed for proper communication with user system.

Power interface: transform external power source voltage to voltages needed for display operation, according to different military standards.

Video signal interface electronics: transforms used video signal formats to the signal compatible with AMLCD driving electronics.

Sensors: usually used to sense display temperature, illumination level or colour, and produce signals used in the display automatic control functions.

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3 DISPLAY BASIC PROPERTIES The main purpose of any display is to show visual information (for human visual system, HVS). Display parameters should be controllable, defined to provide unambiguous requirements of display suitability in intended application.

It is possible to define suitable display characteristics and performances. A specific application needs specific requirements and measurement methods.

Information capacity. The amount of visual “information” that a display is able to convey is related to the “information content” of a display. It is defined by the total number of pixels, the size of the pixels (resolution), colour, the number of grey levels and the size of the display. On the other hand, there is the eye’s ability to discern details - our visual acuity [16] and limitations of human perception.

The acuity of an average human eye can resolve an individual pixel of approximately one arcminute of the visual context wide, with additional conditions attached. Visual acuity determines the level of detail that an eye can absorb from the pattern of pixels present on a screen. The closer the object being viewed, the smaller the level of detail can be determined.

Brightness (Luminance). The brightness of a viewed object is defined in a psychological sense as the level of light intensity perceived by a viewer.

The key physical measure of brightness is luminance.

Brightness is defined as the luminance of white colour in the centre of the screen and is measured in candela per square metre (cd/m2 = nit) or foot-lamberts (1fL = 3.426 nits).

The display luminance value required for comfort viewing varies from 100 cd/m2 in a shadowed office environment up to 1000 cd/m2 in high ambient illumination environment which need not be the threshold quality factor.

Typical AFV display maximal luminance value is up to 500 cd/m2.

For display technologies the other important consideration is the luminance dynamic range (dimming range), that is, the ratio between the minimum and maximum luminance that can be generated, and allow display luminance to set value in accordance with human eye accommodation properties. AFV displays have dimming typical range up to 1:200 in day light operating condition and similarly in night operating conditions, if applied.

Contrast. Display contrast ratio is the ratio of maximal luminance to minimal luminance that can

be generated in the same point in image. Display contrast is created by the difference in luminance from two adjacent surfaces. It is related to display image detail luminance (L) and background luminance (Lb) (usually defined as: (L - Lb) / Lb)).

These parameters should be specified in a predefined illumination environment where ambient light and reflections from the screen will significantly affect the values.

A display may not be able to deliver a “pure” black because the technology applied leaks light or reflects ambient light. A good display will offer a contrast ratio that exceeds 1000:1 measured in dark.

HVS ability to see details at appropriate contrast levels (contrast sensitivity), required contrast which vary around 50, but higher values provides better reproduction of black, proportional to the grey shades values.

Contrast ratio greater than 5:1 is required as the minimum for image details detection in the high ambient light environment usually sufficient as 5.66:1, depending on the mission. In this case black and other colours are “washed up”.

Colour Properties. An average human eye can perceive millions of different colours. The 1931 Commission Internationale de l’Eclairage (CIE) developed a three dimensional colour “space” that allowed any visible colour to be mapped. Any colour could be located within the colour space and its composition from each of the three primaries (Red, Green and Blue) can also be determined.

Display colour reproduction ability depends on the quality of display primary colours. It is usually represented by a triangle in the colour space having red, green and blue colour in the corners, also known as the colour gamut. Display gamut is compared with standard gamut (NTSC) and gamut quality is defined as ratio of display gamut area and standard gamut area in (u’, v’ - CIE 1976) chromaticity chart.

Emissive colour displays usually have more pure primaries and hence wider gamut that non-emissive.

Trade-off between LED’s emission characteristics and colour filters is also important as the issue of this technology, but beyond the contents of this paper.

Resolution. The key measure for display quality, in accordance with HVS acuity is the pixels density expressed in pixel per inch (PPI) or pixel per millimetre (PPMM). This depends on the available components and customer requirements. The requirements for display resolution depend on the application through anticipated observer to display distance. Some typical pixel densities are:

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•

300 PPI (12 PPMM) is typical visual acuity limit for hand held device displays (retinal displays), • 170 PPI (7 PPMM) visual acuity limit for displays is the best in the avionics technology as a comparison, but not required for vetronics, • 200 PPI (8 PPMM) is a good approximation of the HVS requirement within a computer graphical display.

Display resolution 100 to 150 PPI, is sufficient for most AFV display applications.

Active Area. Active area is a display surface where information content is presented. It is measured by diagonal (usually expressed in inches or mm), and aspect ratio (optional technology possible as ratio 1:1, 5:4, 4:3, 16:10, 16:9). AFV mostly displays use standard 4:3 aspect ratio, but different size pending on application. Usually, it is not necessary to resize COTS AMLCD panels. The most common COTS display size and resolution considered for AFV display applications are presented in Table 1.

Table 1. AFV Display Commonly used size and resolution Diagonal

Resolution VGA

SVGA

Orientation XGA

Land.

5” (12.7 cm) • • 5.7” (14.5 cm) • • 6.5” (16.5 cm) • • • 8.4” (21.3 cm) • • • 10.4” (26.4 cm) • • • 12.1” (30.7 cm) • • VGA (6140×480) SVGA(800×600), XGA (1024×768)

Port.

• •

There are a variety of COTS panels suitable for ruggedisation. Some of them are successfully applied in current designs. The 10.4” (26.4 cm) XGA AMLCD display is dominant in current MFD applications.

Proper display size availability is system designer issue, and is limited by AFV. Viewing Envelope. The angle of view is defined as the angle at which the viewer is positioned in relation to the screen in order to clearly see the whole image on a display. The angular viewing envelope is the space that includes all the required viewing angles.

AFV display usually has a viewing envelope that normally covers at least ±60° horizontally and +30°/ –20° vertically, but more specific requirements could be set according to application.

Response-time. The time an individual pixel or cell in a display screen takes to change from open to close and reverse, is known as the response time and is measured in milliseconds, [ms]. The response time affects the ability to change an image rapidly on the screen.

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Some typical response time values required are: 25 ms for general computer applications, 12 to 15 ms for TV, sports and gaming, 100 ms in the case of AFV display displaying graphical content.

The above mentioned cases could be satisfactory for the slow changing graphic content.

LCD has an inherent latency time due to the switching of the liquid crystal, which introduces a longer response time than is required by specific applications. Also, switching time highly depends on temperature. To operate at low temperatures LCD requires uniform heating.

Sun-Readability.

AFV display typical requirement is readability in a high ambient lighting from a low as zero to a high as 10,000 to 50,000 lx of diffuse and/or collimated illumination from one or more directions. The display should be mounted to minimize the impact of the ambient illumination, which is hard to achieve. The display front end should be optically enhanced to minimize diffuse and specular reflectance.

For “mission critical” display a high ambient illumination requirement is usually specified through threshold contrast ratio [18] in given illumination environment (Collimated source generating illumination up to 50,000 lx (5,000 fc), wide diffusive source with luminance up to 6,800 cd/m2 (2,000 fL)).

The measurement method and set-up should be clearly defined. The minimally required contrast value depends on type of information displayed (2 - alpha numerical; 3 - graphics; 4.66 (6 2 grey levels) for B/W image) [17].

NVIS Compatibility. To obtain the possibility to use both display unit and NVG (Night Vision Goggle) at the same time (night driving), a specific technical solution is selected. By using special optical filters on NVG and display unit, the haring of optical spectra is achieved. NVG are filtered using appropriate filters, and a display unit is filtered to eliminate excess of NIR radiation, so the display can be operated successfully using the naked eye, and without disturbing NVG [18]. A display used in NVIS compatible mode has limited gamut (“poor” reproduction of red).

In addition, the display should not disturb the crew NVG during night operations. Also, secure lighting generates additional requirements.

Electromagnetic Compatibility. To provide proper EMC display electronics are equipped with EMI filters, and display active area is covered with a transparent conductive layer (ITO or micro mesh).

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Environmental Properties. A wide operation temperature range is the most critical environmental requirement.

Operation at low temperatures (down to –46 °C) could be achieved by using heaters, but operation at high temperatures should be inherent to display technology. Some of the COTS AMLCD panels are tested at extreme operation temperature range from –30 to +80 °C and storage temperature range –40 to +85 °C, but less range also has enough good reserve tolerance fields.

4 DISPLAY TECHNOLOGIES The simplified classification of the flat panel display technologies is shown in Fig. 6.

An emissive display is one that produces its own light; a passive (non-emissive) display modulates light that passes through it.

Fig. 6. Flat Panel Display classification

4.1 Emissive Display Technologies CRT, Cathode Ray Tube [16]. CRT are not suitable for the AFV applications because they are expensive, not usually available and too large. CRT technology has a historical role but is not considered as suitable for new designs.

FED, Field Emission Displays. FED use electrons to directly fire-up a phosphor screen, in the same manner as traditional CRTs. However, with field emission devices, the mechanism used to generate the electrons is completely different. It is non-thermion and uses the physical properties of “field emission effect” and “quantum tunnelling”,

whereby a low voltage is applied to a very large number of tiny, highly pointed cathodes in order to release electrons. These cathodes can be made from a number of possible materials including carbon inks, diamond-based structures, Spindt tips (molybdenum) and carbon nanotubes. Carbon nanotubes are one of the new products emerging from the field of nanotechnology. FED technology is an interesting solution but still not close to mass production. This technology is not available on the commercial market yet, but it is expected to be soon.

LED, Light Emitting Diode. LED light intensity is proportional to the bias current and the colour dependent on the material used. LED display units are based on matrix of individual emitters. To achieve small pixel size is hard and the production process is very expensive. LEDs are commonly used in backlights and for small dedicated function displays.

ELD, Electro-Luminescent Displays. A phosphor film between glass plates emits light when an electric field is created across the film, and is known as the base for the so called ELD technology [20]. This technology type is effectively singlesourced, monochrome, difficult to obtain video and power hungry – an obsolete technology.

PDP, Plasma Displays. Plasma screens are composed of millions of cells sandwiched between two panels of glass.

PDP technology is suitable for high display size (diagonal higher than 32” (81.3 cm)), so there is no application in AFV displays.

OLED, Organic Light Emitting Diode. OLEDs use a very thin film of an organic substance that can emit red, green, blue or white light when a charge is applied. Display devices are made up of layers of this organic material sandwiched between a positive (anode) layer and a negative (cathode) layer. OLED technology has the potential for large-scale production using printing processes and it is believed it would overcome some of the limitations of LCD [21].

These characteristics, particularly the low power consumption, made OLEDs as promising for smaller display screens and they are already being used in handheld devices.

4.2 Non-Emissive Display Technologies LCD, Liquid Crystal. A liquid crystal material, acting likes a shutter: blocks, dims, or passes light unobstructed, depending on the magnitude of the electric field across the material. It is used in connection with the backlight providing controlled light output from display.

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To form a working LCD individual components (glass casing, liquid crystal cell, alignment layer, conductive electrodes, and polarizer) are combined.

The light entering the display is polarised by back polarizer, and interact with oriented liquid crystal molecules. When voltage is applied, the liquid crystal molecules orientation is changed causing the liquid crystal polarisation properties. As a result of interaction with second polarizer the luminance of the output light could to vary from minimal to maximal value pending on voltage applied. A colour filter is applied to provide colour sub-pixel.

High-end displays today easily have 256 different levels of light or shades allowing a grey scale range in which graphics and characters can be displayed in many varying intensities [19].

AMLCD Basic Technologies defining the AMLCD panel structure and functioning are Twisted Nematic (TN), – Super Twisted Nematic (STN), Vertical Alignment (VA), Multidomain Vertical Alignment, (MVA) In Plane Switching (IPS), Advanced Field Fringe Switching (AFFS).

TN (STN) displays have a narrow viewing envelope. To achieve a wide viewing angle, additional optical compensation films are used.

VA and IPS technology provides wide viewing angle.

Micro Electro Mechanical Systems (MEMS) and Projection Display. MEMS are miniature devices, which integrate actuators, sensors, and processors to form intelligent systems. Functional optical sub-systems controls light transmission or reflection. There are few emerging DLP technologies still in development (Grating valve display, Pixtronix MEMS shutter with Field sequential RGB backlight, Mirasol displays based on bi-stable interferometric modulation).

Combined with a digital video or graphic signal, a light source and a projection lens, the mirrors of the DMD chip can reflect an all-digital image onto any surface.

DLP Projection displays are too bulky for AFV applications. Other MEMS display technologies are not ready for mass production and application.

4.3 Ruggedisation Technologies There are various ruggedisation techniques applicable to enhance display properties, such as: Optical Bonding. One of the most important is optical bonding that allows us to join different layers (glass, filters, or films) to enhance display rigidity and display front end optical or conductive properties.

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The resultant assembly is very rugged, shock, impact and vibration resistant and maximizing optical properties at the same time. Two main technologies used for optical bonding are: (i) liquid bonding (using silicones, epoxies, polyurethane) – Optically Clear Adhesive (OCA) and (ii) dry bonding (using roll on process based on application of pressure and heat activated dry adhesive sheets.

Resizing. To allow that AMLCD COTS displays could be used in applications requiring specific shape, resizing process has been applied. This is rather complicated [22] and [23], and protected with patents.

Resizing has an important role in AMLCD technology application mainly in cockpits, but could be used in any other application.

EMI Shielding. EMI interference could be critical in the AFV environment. There are several techniques suitable and proved for EMI shielding optimization: (i) EMI filtering on the PCB; (ii) proper grounding techniques; (iii) transparent conductive layer over display active surface (ITO or micromesh), forming proper Faraday cage together with metal housing.

4.4 Touch Panel Technologies Touch Panel – Screen is a position-sensitive device, which could be activated using finger or stylus. At the same time, they are transmissive and could be overlaid t display active surface. This allows integration of the display visual content and touch position detection into unique human machine interface capability. This capability makes them very suitable as data input device for mobile applications.

To be considered as suitable for integration, touch panels should have sufficiently high optical clarity, transmission and touch position sensing resolution.

The major benefits of the touch technologies are: (i) easy to use – what you see you touch to generate command, (ii) flexible – Using the same interface one can implement different options, (iii) upgradeable – easy and fast changes through software, (iv) cost effective – this is a relative issue depending on application, (v) rugged and reliable performances – could be considered for use in an extremely harsh environment.

Having in mind the promising capabilities, a lot of efforts have been made in the development of suitable technologies. Some of them are applicable in AFV displays: • Resistive (RES), • Capacitive & Projective Capacitive (CAP and PCAP),

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• •

Surface Acoustic Wave (SAW), Infrared Array Sensor (IR).

A comparison of applicability properties of touch screen technologies in military environment is shown in Table 2.

Table 2. Touch Screen Technology Comparison Benefits

Touch panel technology IR RES CAP SAW Vandal Resistant ••• •• •• •• Scratch Resistant ••• • •• •• Not sensitive to dirt •• ••• •• • Non Sensitive to EMI ••• ••• • • Can be FINGRER operated ••• ••• •• •• Can be GLOVE operated ••• •• •• •• Can be hermetically sealed ••• ••• ••• •• Sensitivity to temperature ••• •• ••• ••• Suit military environment ••• •• ••• ••• Integration ••• •• ••• • NVIS compatibility • ••• ••• ••• ••• excellent , •• acceptable, • bad

5 AFV DISPLAY TECHNOLOGY EVOLUTIONS CRTs were used in AFV fire control systems to display sensor (TV or thermal imager) image integrated with reticule and other sighting related data.

Multifunctional and moving-map displays were the first objectives which generated new developments using any new technology available.

Electroluminescence panels were introduced as the first all solid state based displays, well suited to AFV environment. Relatively low brightness (about 50 fL as the extreme values probably reduced on the half by filtering) high panel production price together with lack of colour TFEL in mass production were the key disadvantages that contributed to their low application as future AFV displays.

Introduction of AMLCD for avionics in the mid 1980s, as feasible technology was an example how these technologies cold find application in the demanding environments as aircrafts and AFVs are.

After that AMLCD application spread in all other military applications, including AFV related displays.

In the 1990s, display devices research and development were accelerated and long term development road-map was set down [14]. AMLCD panel storage, start up were the less problems but the main have been operating temperature.

The LC materials remain operable, although slower, down to -30°C and lower. Speed of operation can be increased with heating via a transparent Indium-

Tin-Oxide (ITO) thin-film heater applied close to the AMLCD panel, although not very effective regarding that some sources use non-transparent heater behind BLU. Also, the LED backlight acts as a heater because of its power dissipation contributing to panel surface temperature increase up to 10 °C. The high operation temperature is limited by the clearance point of the LC material. Above the clearance point temperature, an immediate but reversible loss of image occurs. Modern LC materials can be fabricated with a clearance point temperature of over 100 °C without sacrificing other properties, with possibility to trade values vs response time.

The back-lit AMLCD is unique in several ways that prove to be highly desirable attributes for AFV use. The following objectives for AFV displaying instruments are satisfied by the AMLCD: i. Low volume with low weight and power preferably without forced air cooling; ii. Wide luminance range is easily achievable (from 0.1713 cd/m2 to as high as 685.2 cd/m2); iii. Colour primaries of saturated red, green and blue with up to 256 shades of grey in each primary, but usually taken as lower values of 64 shades. iv. Wide viewing angle greater than ±60° in both horizontal and vertical direction, also variable by trade-off in vertical direction. v. Readability in high ambient illumination with contrast ratios of at least five to one. This depends on the internal design and the definition of high ambient illumination. vi. Sufficiently uniform brightness through the image plane without distortion, and acceptable resolution with at 100 to 150 PPI pixels density, variable by supplier’s options and cost. vii. Response speed suitable for frame rates up to 80 frames per second.

6 CONCLUSIONS AFV vetronics systems are still not fully defined, but results from current research could be used in AFV upgrade programs, as well as for future hybrid electric heavy duty vehicles [24].

AFV display technologies are limited only to what the COTS sources can supply. Being the elements of ubiquitous computing systems [25], they allow AFV system integrator to specify proper requirements delivering desirable HMI functions.

CRT displays were only used for essential video sighting functions. They introduced image application in AFV control stations increasing display information capacity.

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ELD (TFEL) and LED displays find their place in some specific application opening the door to all solid state displays.

Back-lit AMLCD shows up as ideal for application in AFV systems. Nowadays, there is no display technology that comes close to compete with AMLCD availability, performance and price.

Liquid crystal development forced by TV related application, contributed to increase LCD speed and viewing envelope. Hand held and industrial application contributed more or less to increase in clearance temperature.

AMLCD market is fast evolving in the area of mobile displays, computer and laptop monitors, but it is stable in the area of industrial and special application displays. AFV display suitable sizes and resolutions are possible to be covered with industrial display panels, depending on commissioner.

The AMOLED displays are a new and competitive technology, having mass production for small area mobile displays, and emerging application as TV displays, but it will not be ready for mass production for sizes suitable for AFV vetronics systems in the next five years. The first application of this technology could be for personal AFV crew displays.

Resistive touch screen has some applications in AFV displays, but there are issues with life time. Also, there is a need for more research regarding human factors affecting their effective usage as HMI device in military environment.

AFV vetronics systems designers could count on COTS AMLCD panels and ruggedisation process to provide suitable AFV displays in various Crew Station configurations.

There are new display technologies under development but it seems that none is ready enough to replace AMLCD technology in AFV application during this decade.

7 ACKNOWLEDGEMENT This work has been done within the project III 47029 supported by Ministry of Science and Technological Development of the Republic of Serbia.

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 386-393 DOI:10.5545/sv-jme.2011.278

Paper received: 2011-12-20, paper accepted: 2012-04-25 © 2012 Journal of Mechanical Engineering. All rights reserved.

Acoustic Experimental Data Analysis of Moving Targets Echoes Observed by Doppler Radars Andrić, M. – Bondžulić, B. – Zrnić, B. – Kari, A. – Dikić, G. Milenko Andrić1,* – Boban Bondžulić1 – Bojan Zrnić2 – Aleksandar Kari1 – Goran Dikić1 1 University of Defence, Military Academy, Belgrade, Serbia 2 Ministry of Defence, Defence Technology Department, Belgrade, Serbia

In this paper we describe the main tasks of ground surveillance radars for security and perimeter protection and targets detection. Our goal is to provide a balanced and comprehensive database to enable reproducible research results in the field of classification of ground moving targets (pattern recognition).

Also, in this paper, we consider received radar echoes data of ground moving targets, and corresponding signals in time – frequency domain using spectrogram and cepstrum. The database, noted as RadEch Database, containing radar echoes from various targets. The objective of the paper is to identify and validate the intrinsic features characterizing the different classes of targets, and subsequently extract salient features for classification Keywords: cepstrum, classification, Doppler signature, feature extraction, radar echoes database, spectrogram

0 INTRODUCTION The main tasks of ground surveillance radars for defence and specific perimeter protection are detection and classification of ground moving targets.

This process usually takes electro magnetic (EM) radars as the base sensors and Doppler effect to estimate radial velocities. EM radars, as sensors, are a well known technology for different surveillance and measurement purposes. Signal processing of EM radars shows some advantages if it transforms into the acoustic audio signals to the end users. Signals from EM radars are very sensitive on the jamming which causes difficulties in terms of its processing, digitalization and final recognizing of their sources.

Acoustic signature as a diagnostic tool has different applications in mechanical engineering [1] and distribution of acoustic waves, its form and characteristic properties initiate different methodologies to estimate [2] behavior and performances of required reflected targets, spare parts, mechanical elements, environmental areas, and components, etc. Due to the above mentioned, in the most applications of ground surveillance radars, moving targets classification is performed using their transformation of EM signals to acoustic in aim to estimate audio-Doppler signature.

The Doppler phenomenon describes the shift in the center frequency of an incident waveform due to the target motion with respect to the radar [3]. Radar produces an audio signal from the Doppler frequency of moving targets. Important classes of ground targets can be distinguished by their audio Doppler signature.

While the operator recognizes the moving targets using the audio Doppler signatures by listening an 386

audio channel, this concept leads to unsatisfactory performance, limited by the human operator’s senses.

In aim to avoid this, miss data base of acoustic signatures transformed from EM radar signals in the loop, is necessary.

To the best of our knowledge, there is only one database with a wide class of target echoes for low resolution surveillance radar. However, there are differences between database description given in [4]. Therefore, extensive experiments with various scenarios were carried out, represented in this paper, in order to obtain such a database (different targets and environments).

The second problem to achieve reliable data about those targets in using audio signals from EM radars is the method of signal processing and recognizing types and states of the targets.

Many current radar-based classification systems employ some type of Doppler or Fourier-based processing, followed by spectrogram and gait analysis to classify detected targets.

In several studies it has been proved that spectrogram-based features could be used for discrimination purposes either between humans and other moving objects or between different persons [5] to [8]. Human spectrograms can be used to reveal information on human behaviour and to determine features about the human target being observed, such as size, gender, action, and speed, too.

Research done in [5] had shown that the human spectrogram is the sum of Doppler shifted signals.

Using Short Time Fourier Transform (STFT) and the chirplet transform, they extracted various parameters of the human gait from the signal. Research done in [6], has shown that the radar Doppler signatures

*Corr. Author’s Address: University of Defence, Military academy, Pavla Jurišica Šturma 33, Belgrade, Serbia, asmilenko@beotel.net

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 386-393

give detailed information about the movements of the human body parts. The authors focused on the extraction of parameters and described a method for estimating human walking parameters from radar measurements. The application of continuous-wave radar for the detection and classification of people based on their motion has been demonstrated in [7]. Spectral analysis of the output from the radar using a sequence of STFTs was used to extract and to identify some key features of the human walking motion, and to differentiate humans from dogs. Using human gait analysis [8] designed and tested a suicide bomber detection system based on variations in the spectrogram caused by the presence of a bomb.

A target classification algorithms using Doppler signature were presented in [9] to [13]. In [9] a Hidden Markov Model (HMM) classifier was implemented for classification between three classes of targets: personnel, tracked vehicles and wheeled vehicles. A fuzzy logic approach to the automatic classification was presented in [10]. The problem of classification between a walking person, pair of walking persons and slowly moving vehicle was studied in [11].

Time varying velocities and bio-mechanical human locomotion models they used for target classification.

At first glance, cepstrum-based features seem like a promising solution for classification problems.

However, the applicability and performances of these features were sometimes not tested in the context of practical systems [12]. Therefore, extensive experiments with various scenarios were carried out in order to obtain a radar echoes database (different targets and environments). In order to identify and validate the main features of the various target classes the STFT and cepstrum analysis are performed.

The basic goal of this paper is presentation of autonomous measured data base and an appropriate method of signal processing for targets recognition, tracked by EM radar, linked with a audio sensor to the end user, as the base for digitalization in a further automatic awareness system.

1 TARGETS DATABASE DESCRIPTION AND COLLECTION The database was obtained using records of short range ground surveillance radar, collected on the memory of computer. This radar is coherent and has from the outset possessed a so called audio output which can be used by the operator to classify targets.

When a radio frequency (RF) signal is incident on a target moving towards or away from the radar, the signals reflected from the various components of the

target will have a Doppler shift that is proportional to the velocity of those components.

The radar operates in the Ku-band and for this carrier frequency, the Doppler frequencies lie within the audio band, being of the order of a kilohertz, and so can be presented as an audio tone to the radar operator, via headphones. Listened or signed tone was noted that ground moving targets produced a very distinct and characteristic sound that, upon hearing it only a few times, it is easily recognized.

The target sensor, used in database collection, is 16.8 GHz ground surveillance pulse-Doppler radar.

The radar parameters are: average power is 5 mW, pulse width 15 µs, average range resolution 150 m, elevation resolution 7.5°, and azimuth resolution 5°.

For the recording procedure, the target was detected and tracked automatically by the radar, allowing continuous target echo records. The range between the radar and the target was set to be short (100 to 1000 m). The moving targets were within the line-of-sight, in the presence of ground clutter with low vegetation and without any interference. The target motions were fully controlled. One target at a time was recorded in each scenario.

Fig. 1. Principal scheme of Doppler radar

Amplitude of the raw radar data was in the range ±1 V and the sampling frequency was 4 kHz. Audio signal from the radar was connected to laptop sound card microphone input. The radar’s baseband audio signal was recorded onto a laptop, where the data was then saved as digitized WAV files. This allowed for the data to be easily processed using MATLABTM. The large database of the raw real audio Doppler signals was created through more than 80 different scenarios. The targets were recorded in two different environments. The first environment is the road of 4 m width, and 800 m length. The second environment is the rough terrain, with barriers (slews, woods), and with small vegetation. Targets from the following classes were recorded: 1. Person and group of persons - combinations of the following cases were represented in the collected database:

a. Number of persons: 1, 3 or more.

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b. Motion: crawling, normal walking, and

running.

c. Synchronous / asynchronous motion of

persons in a group.

d. Pedestrian, soldier, group of persons, group

of soldiers.

e. Go away - from the radar (otherwise toward

the radar).

2. Vehicle:

a. Wheeled / Truck vehicle.

b. Speed of motion: normal (20 to 30 km/h) and

fast (30 to 60 km/h).

3. Vegetation clutter (trees, bush).

The database that was collected during this work is available at [14].

2 SPECTROGRAM-BASED ANALYSIS OF AUDIO DOPPLER SIGNAL Radar target classification has been an active research area. Usually, a feature extraction process plays an essential role for the success of target classification.

Due to the highly aspect-dependent nature of the scattered signature, a feature extraction for target classification is an especially difficult problem [10] and [15]. The feature extraction was obtained using a short-time Fast Fourier Transform (FFT).

The most standard approach to analyze a signal with time-varying frequency content is to split the time-domain signal into many segments, and then take the Fourier transform of each segment. This is known as the STFT operation and is defined as:

X n (e jω ) =

∞

∑ w[n − m]x[m]e

− jω m

.

(1)

NFFT is the number of FFT points used to calculate the discrete Fourier transform, and:

 N x − NOVERLAP  m = fix  ,  LWIN − NOVERLAP 

(3)

where Nx is the input sequence length, NOVERLAP the number of samples each segment of input sequence overlaps, LWIN the length of window function, and function fix rounds to the nearest integer towards zero.

The Kaiser window function length of 256 and with parameter β = 3π was applied. Overlapping between adjacent windows was 128 samples (NOVERLAP = 128). Maximum Doppler frequency is equal 2 kHz. Radar target echoes spectrograms of clutter, person walking, person running, walking group, running group, and light wheeled vehicle, are presented in Fig. 2. The Doppler frequency is displayed on the vertical axis and time on the horizontal. The amplitude of the reflected signals grey scale coded with the highest intensity and the lowest. Each target class has unique time-frequency characteristics, which can be used for classification.

The Doppler frequency shift from a target moving with a velocity vr along the line-of-sight of the sensor is:

m =−∞

In Eq. (1), w[n-m] is a real window sequence which determines the portion of the input signal that receives emphasis at a particular time index, n. The time dependent Fourier transform is clearly a function of two variables: the time index, n, which is discrete, and the frequency variable ω, which is continuous.

The magnitude display |Xn(ejω)| is called the spectrogram of the signal. It shows how the frequency spectrum (i.e., one vertical column of the spectrogram) varies as a function of the horizontal time axis. In most applications for classification of radar echoes Doppler signals, spectrogram is an often used solution.

Based on spectral analysis of Doppler signal by spectrogram, central Doppler frequency and width of spectral band around it are possible features for fuzzy variables [11].

388

The time-frequency analysis of collected signals was performed by a spectrogram. Spectrograms are calculated for the audio Doppler sequences length of 4 seconds (16000 samples).

Spectrogram is represented by n×m matrix where are: NFFT (2)

n= + 1.

2

fd =

2 vr

λ

,

(4)

where λ is the sensor wavelength. One limitation of this type of sensor is that it cannot distinguish whether the object is moving towards or away from it, hence there is absolute value.

The clutter signature (Fig. 2a), which is moving vegetation outcome, is located on frequencies below 100 Hz. An example of Doppler spectrogram from a walking person is presented in Fig. 2b. When humans walk, the motion of various components of the body including the torso, arms, and legs produce a very characteristic Doppler signature.

Human walking motion is quite complex with contributions to these velocity components from each of the upper and lower parts of the extremities. For

Andrić, M. – Bondžulić, B. – Zrnić, B. – Kari, A. – Dikić, G.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 386-393

a)

b)

c)

d) e) f) Fig. 2. Spectrograms of radar echo target samples: a) clutter, b) person walking, c) person running, d) vehicle, e) group of persons walking, and f) group of persons running

a) b) c) Fig. 3. Spectrograms of a person radar echo samples; a) crawling, b) walking on the road, c) walking on the bush

a person walking with a constant velocity, the signal reflected from the torso, will have a constant Doppler shift. The signals reflected from the swinging legs and arms, will be modulated at the cadence frequency, which is the step or leg swing rate. In general, the arms and legs will have the same periodicity since the arms swing to counterbalance the legs [7].

In Fig. 2b the torso component has a nearly constant Doppler frequency of about 200 Hz indicating the person was moving with a speed, using Eq. (3), of about 1.75 m/s. The leg swings introduce a nearly sawtooth modulation around of this torso component.

The dominant contribution to the Doppler signature appears to be the motion of the torso and the legs, the contribution of the arms is not as dominant.

The motion of the torso produces a steady Doppler shifted signal, which is modulated by the

motion of the swinging arms and legs that results in a Doppler signature which is very characteristic of humans.

The envelope of the curve corresponds to the motions of the legs and arms, which have smaller cross sections than the torso, so they are less detectable at a distance.

Doppler spectrogram from a running man is presented in Fig. 2c. There is a specific man signature which is characterized by the low Doppler frequency and with a component which oscillates in frequency (characteristic quasi-periodic signal).

A walking person Doppler signature usually lies from 100 to 300 Hz, and a running person Doppler shift lies from 350 to 600 Hz. The comparative analysis of spectral characteristics of these two target classes shows a

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difference in central Doppler frequency and the width of the spectral line around central Doppler frequency.

As the speed of man increases, central Doppler frequency and the appropriate spectral band width also increase.

As the number of persons in a group increases, irrespective of motion type, the spectral band widths also increase (Figs. 2e and f).

A spectrogram from light-wheeled vehicle (car) is seen in Fig. 2d. The signature from moving wheeled vehicle has one dominant spectral line (Doppler frequency) and narrow band of spectral components around central Doppler frequency because the wheeled vehicle is a compact target without moving subreflectors. Tist is the reason for the sound like a pure tone in the operator’s headphones. The target has a nearly constant Doppler frequency of about 1400 Hz indicating the car was moving with a speed, using Eq. (3), of about 12.5 m/s (45 km/h).

As a conclusion, the band of spectral components around central Doppler frequency is the smallest in the case of a wheeled vehicle in comparison with the walking and running man case. Consequently, in the case when central Doppler frequencies of a running man and a wheeled vehicle with low velocities are similar, they may be used to resolve this type of classification conflict the width of spectral band around the central Doppler frequencies.

Target signature may significantly vary from one scenario, which is illustrated in Fig. 3, where are spectrograms of a crawling person, a person walking on the road, and a person walking in the bush, are shown.

A crawling person spectrogram, (Fig. 3a), is periodic, but with pauses, due to type of motion.

In Figs. 3b and c the torso component has a nearly constant Doppler frequency of about 200 Hz. Audio echoes are modulated with ambient conditions.

The leg swings are hidden with vegetation in Fig. 3c.

3 CEPSTRUM-BASED ANALYSIS OF RADAR ECHOES A cepstrum is the result of taking the inverse Fourier transform (FT) of the log spectrum as if it were a signal. Its name was derived by reversing the first four letters of spectrum. There is a complex cepstrum, a real cepstrum, a power cepstrum, and phase cepstrum.

The cepstrum c[n] of a discrete-time signal x[n] is defined as [12] and [13]:

{

}

c[n] = F −1 log ( F { x[n]}) ,

where F[×], and F-1[×] are the Discrete Fourier and the inverse Fourier transforms, respectively.

In Fig. 4 are shown first sixteen significant real cepstrum coefficients for same sequences used in spectrogram analysis. Values of the rest of the coefficients are very small and they are not showed.

Generally, cepstrum concentrate energy in few cepstrum coefficients values.

In this paper we analyzed a dependence of cepstrum coefficients from central Doppler frequency and spectral width around it throught two experiments.

In first experiment we analyzed a dependence of cepstrum coefficients from central Doppler frequency.

For this purpose we used 20 sequences from each of three major group of moving targets (one person, group of persons and vehicle). All these sequences we grouped in three classes based on central Doppler frequency: below 300 Hz, between 500 and 700 Hz and above 1400 Hz. We varied sequence duration from 0.125 to 2 s. Number of points used to calculate the Discrete Fourier transform is 1024.

Cepstrum coefficients are widely used in speech and speaker recognition applications and we applied them to the radar data. For the illustration purposes, samples of the second and the third cepstrum coefficients are analysed in Fig. 5.

a) b) c) Fig. 4. Real cepstrum coefficients of radar echoes target samples; a) person walking, b) group of persons running, c) vehicle

390

(5)

Andrić, M. – Bondžulić, B. – Zrnić, B. – Kari, A. – Dikić, G.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 386-393

In Fig. 5 are presented projections of the second and the third real cepstrum coefficients for three analysed classes and for different sequence durations.

From Figs. 5a and b can be concluded that there is no significant difference in the second and third real cepstrum coefficients values for 1 and 2 s sequence durations. In these values information about central Doppler frequency is kept, which is one of the major characteristics for classification.

Furthermore, as the sequences duration decrease, the second and the third real cepstrum coefficients from various classes are closer (see Fig. 5c). This can be explained with the fact that there is no enough information for proper separation of classes.

In the second experiment we used 20 sequences from each of three major group of moving targets (one person, group of persons and vehicle). All these sequences were grouped in two classes based on spectral width: below 40 Hz and above 100 Hz. Sequence duration from 0.125 to 2 s, too. The same number of points used to calculate the discrete Fourier transform as the first experiment.

In Fig. 6 projections of the fifth and the sixth real cepstrum coefficients for two analysed classes and for different sequence durations are presented.

From Figs. 6a and b it can be concluded that there is no significant difference in the fifth and sixth real cepstrum coefficients values for 1 and 2 s sequence durations. In these values is information about spectral width around central Doppler frequency is kept, which is one of the major characteristics for classification.

Furthermore, as the sequences duration decrease, the fifth and the sixth real cepstrum coefficients from various classes are closer (see Fig. 6c). This can be explained with the fact that there is not enough information for proper separation of classes.

4 CONCLUSION In this paper the database of radar echoes from various targets has been described. The database is available for public download.

The spectral analysis conducted in this paper is used to extract very basic information that could be used for classification. It was not intended to identify individuals or classes of people from their gait. More sophisticated techniques would be needed to resolve the contributions to the gait motion from body parts like the arms, upper leg, lower leg, and foot.

We believe that such a publicly available database will allow easier comparison and performance evaluation of the existing and future classification algorithms.

Fig. 5. The second and the third real cepstrum coefficients for different sequence duration; a) 2 s, b) 1 s, c) 0.125 s

In future work we will extend our database with new target classes (tanks, helicopters, animals). We will also provide a database for target detection and classification research.

Also, we developed and analyzed cepstrum coefficients of the real audio (acoustic) radar signals.

It has been showed that the second and the third cepstrum coefficients give promising information

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 386-393

5 ACKNOWLEDGMENT Results presented in this paper are made within project No 47029 financed by the Ministry of Science and Technology Development, the Republic of Serbia.

6 REFERENCES

Fig. 6. The fifth and the sixth real cepstrum coefficients for different sequence duration; a) 2 s, b) 1 s, c) 0.125 s

about central Doppler frequency, while the fifth and the sixth cepstrum coefficients give promising information about the spectral width around it. The cepstrum-based analysis conducted in this paper is used to extract very basic information that could be used for target types estimations. In future work we will use these notices to develop cepstrum-based classification algorithms and to develop further job for automatic recognizing software and hardware.

392

[1] Virtić, M. P., Aberšek, B., Župerl, U. (2008). Using of Acoustic Models in Mechanical Diagnostics. Strojniški vestnik – Journal of Mechanical Engineering, vol. 54, no. 12, p. 874-882.

[2] Solodov, I., Doring, D., Busse, G. (2011). New opportunities for NDT using non-linear interaction of elastic waves with defects. Strojniški vestnik – Journal of Mechanical Engineering, vol. 57, no. 3, p. 169-182.

[3] Avci, E., Turkoglu, I., Poyraz, M. (2006). A new approach based on wavelet nero genetic network for automatic target recognition with X-band Doppler radar. Journal of Electrical & Electronics Engineering, vol. 6, no. 2, p. 157-168.

[4] Bilik, I., Tabrikian, J. (2007). Knowledge-based target classification for Doppler radars in knowledge-based radar detection. Gini, F., Rangaswamy, M. (eds.)

Tracking, and Classification, John Wiley & Sons, Hoboken, ch. 9, p. 197-224 [5] Geisheimer, J.L., Marshall, W.S., Greneker, E. (2001). A continuous-wave radar for gait analysis.

35th Asilomar Conference on Signals, Systems, and Computers, Conference Proceedings, vol. 1, p. 834838.

[6] van Dorp, P., Groen, F.C.A. (2003). Human walking estimation with radar. IEE Radar Sonar Navigation, Proceedings, vol. 150, no. 5, p. 356-365.

[7] Otero, M. (2005). Application of a continuous wave radar for human gait recognition. Proceedings of SPIE: Signal Processing, Sensor Fusion, and Target Recognition XIV, vol. 5809, p. 538-548.

[8] Greneker, G. (2005). Very low cost stand-off suicide bomber detection system using human gait analysis to screen potential bomb carrying individuals.

Proceedings of SPIE: Radar Sensor Technology IX, vol. 5788, p. 46-56.

[9] Thayaparan, T., Abrol, S., Riseborough, E., Stankovic, Lj., Lamothe, D., Duff, G., (2007). Analysis of radar micro-Doppler signatures from experimental helicopter and human data. IET Radar Sonar Navigation, vol. 1, no. 4, p. 289-299, DOI:10.1049/iet-rsn:20060103.

[10] Jahangir, M., Ponting, K.M., O’Loghlen, J.W. (2003).

Robust Doppler classification technique based on hidden Markov models. IEEE Proceeding-Radar Sonar Navigation, vol. 150, no. 1, p. 33-36, DOI:10.1049/iprsn:20030027.

[11] Andrić, M., Đurović, Ž., Zrnić, B. (2005). Ground surveillance radar target classification based on fuzzy logic approach. Proceedings of International Conference on Computer as a Tool, vol. 2, p. 13901392.

Andrić, M. – Bondžulić, B. – Zrnić, B. – Kari, A. – Dikić, G.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 386-393

[12] Bilik, I., Tabrikian, J., Cohen, A. (2006). GMM-based target classification for ground surveillance Doppler radar. IEEE Transaction of Aerospace and Electronic Systems, vol. 42, no. 1, p. 267-278, DOI:10.1109/ TAES.2006.1603422.

[13] Bilik, I., Tabrikian, J. (2007). Radar target classification using Doppler signatures of human locomotion models. IEEE Transaction of Aerospace and Electronic Systems, vol. 43, no. 5, p. 1510-1522, DOI:10.1109/ TAES.2007.4407474.

[14] The database of radar echoes from various targets, from: http://cid-3aaf3e18829259c0.skydrive.live.com/ home.aspx, accessed on 10-04-21.

[15] McConaghy, T., Leung, H., Bosse, E., Varadan, V. (2003). Classification of audio radar signals using radial basis function neural networks. IEEE Transactions on Instumentation and Measurement, vol. 52, no. 6, p.

1771-1779, DOI:10.1109/TIM.2003.820450.

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 394-402 DOI:10.5545/sv-jme.2011.277

Paper received: 2011-12-20, paper accepted: 2012-04-03 © 2012 Journal of Mechanical Engineering. All rights reserved.

Experimental and Simulation Testing of Flight Spin Stability for Small Caliber Cannon Projectile Milinović, M. – Jerković, D. – Jeremić, O. – Kovač, M. Momčilo Milinović1,* – Damir Jerković2 – Olivera Jeremić1 – Mitar Kovač2 1 University of Belgrade, Faculty of Mechanical Engineering, Serbia 2 University of Defense, Military Academy, Serbia

The basic aim of this paper is to consider correlations of stability flight criteria, derived as the relations of aerodynamic coefficients and derivatives, on the model of a small caliber cannon spin stabilized projectile. Model of stability criteria calculations are performed by experimentally testing of aerodynamic data in the wind tunnel, and composed with the semi-empirical data, both applied on the flight trajectory stability simulation test. Authors’ wind tunnel tests and calculated values of aerodynamic coefficients, as the function of Mach numbers of projectile model, are presented in the simulation flight trajectories stability criteria. The comparative analysis of experimental and calculated aerodynamic coefficients of projectile model is done, and refers to the stability flight criteria. Calculation of projectile aerodynamic Magnus moment derivatives, with other aerodynamic representatives, is used as the critical stability factors testing data vs. flight Mach numbers. Influences of this derivative absence and presence on the model sequence of the flight trajectory are presented for the estimation of angles of attack damping and stability factors. Simulation tests are presented for the supersonic and subsonic integral flight velocities and spin damping data. Research is realized due to the considerations of further projectiles correction possibilities on trajectory, and other new applications, vs. existing of unreliable lateral moments.

Keywords: aerodynamic coefficients spin stabilized small caliber cannon projectile, gyroscopic stability factor, dynamic stability factor, damping stability coefficients

0 NOMENCLATURE CM pitching moment coefficient, Mv/QSd, [-], CMα derivative of pitching moment coefficient,

∂CM/∂α, [-], CMa derivative of pitch damping moment

coefficient due to q*, ∂CM/∂q*, [-], CM α derivative of pitch damping moment coefficient due to α , ∂CM/∂α , [-], CL lift (normal) force coefficient, ‒Fz/QS, [-], CLα derivative of lift force coefficient, ∂CL/∂α,

[-], CN yawing moment coefficient, Mz/QSd, [-], CMpα derivative of Magnus moment coefficient, ∂2CN/∂p*∂α, [-], CD drag (axial) force coefficient, Fx/QS, [-], CD0 zero angle drag coefficient, (CD)α=0 , [-], d reference diameter (caliber), Ix axial moment of inertia, [kg·m2], Iy transverse moment of inertia, [kg·m2], rx relative axial radius of gyration, reversed to

the caliber, (Ix/md2)1/2, [-], ry relative transverse radius of gyration reversed

to the caliber, (Iy/md2)1/2, [-], Fx, Fy, Fz forces along x, y, z axes, [N], Mx, My, Mz moments about x, y, z axes, [N·m], m mass of projectile, [kg], p spin rate, [s-1], p* reduced spin rate, pd/V, [-], Q dynamic pressure, ρV2/2, [Pa], 394

pitch rate, [s-1], q * q reduced pitch rate, qd/V, [-], S reference area, πd2/4, [m2], α angle of attack (pitch), [°], β angle of sideslip (yaw), [°], αt total yaw angle, approx. (α2+β2)1/2, [°], ξ complex angle of attack, α+iβ, [°], atmospheric density, [kg/m3], ρ  velocity vector of projectile, [kg/s], V u, v, w components of velocity along x, y, z axes,

[m/s], H, P, T, M, G Murphy’s coefficients, [-], E = (ρSd)/(2m) reduction mass expression, [-], Sg gyroscopic stability factor, [-], Sd dynamic stability factor, [-], λ1,2 damping stability coefficients, [-]. *

denotes reduction of derivatives Cij* = Cij E .

coefficients

and

1 INTRODUCTION In the last twenty years the modern ammunition design, extended precision technology applications of guidance and control on the lower calibers of tactical ammunition. Analyses to be considered for guidance redesigning are especially challenging for the anti-aircraft (AA) cannon ammunition of smaller dimensions because of specific properties of projectiles flight, which have constraining

*Corr. Author’s Address: University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, Belgrade, Serbia, mmilinovic@mas.bg.ac.rs

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 394-402

possibilities of guidance technologies applications, [1] to [5]. Unguided AA projectile is, primarily, used for air targets, shooting with ballistic trajectories, but new considerations may also suppose its applications for the ground targets engaged from air and ground platforms in the so called close support operations.

Ballistic trajectory of AA gun projectile have significant changes of supersonic transonic and subsonic velocities during flight, from the very high initial to the much lower terminal values in the target impact point. Stable free ballistic flight of projectiles and stability criteria, determines attitudes of projectile axes towards the trajectory, [6] to [8]. It depends on aerodynamic shape, sensitivities on the drag and lift forces, aerodynamic moments their derivatives and spin rate stabilization efficiency vs. flight Mach numbers, but also of less discovered lateral Magnus moment and other artificial designed moments coupled with them, which changes on the flight trajectory.

The importance of experimental aerodynamically accurate estimations coupled with numerical stability criteria simulations is required because the spin stabilized symmetric AA cannon type projectile, exposes sensitive effects on the projectile stability which could influence conclusions about its novel applications and the redesign in the modernization considering processes.

A comparative analysis of calculated and experimental parameters is well known, proceeding for a preliminary estimation of all kinds of flight bodies, including flight vehicles with typical gyro – aerodynamics correlation loads, as in the [9] and [10] as rotary wings flight objects. Spin gyro – aerodynamics correlation loads, which strongly influenced on stability of flight projectiles, are referencing on the second class of flight bodies, known as the projectiles.

This paper deals with the aerodynamics of the spin projectile which is tested in the wind tunnel. The tested aerodynamics is compared with numerically predicted aerodynamic coefficients and derivatives.

Both are used for the stability criteria analysis vs.

Mach numbers.The simulated data are used from the AA gun model trajectory designed in [11] to [13].

2 SPIN STABILIZED CRITERIA AND DATA REQUIREMENTS The key property of spin stabilized projectiles flight could be determined by the quality of its space spherical motion around the projectile body gravity center, during the flight on the ballistic trajectory. A very high spin of longitudinal axis and the low spin

of the lateral disturbance provides gyro moment to stabilize projectile pitch. Composed spherical oscillations of body axes and direction of velocity vector, is question of stabilization [6] and [7]. As a result these lateral oscillations decrease perturbed amplitudes of total angle of attack if spin stabilization is successful, or increase if the projectile has not realized enough initial rpm by spin to form gyromoment for damping. Complex variable of the total angle of attack ξ, and its lateral angular motion due to the projectile body can be described by linearized differential equation derived by dimensionless distance instead of time as the main argument [6] in the form:

ξ ′′ + ( H − iP ) ξ ′ − ( M + iPT ) ξ = −iPG,

(1)

where H, P, T, M and G represents the so called Murphy’s coefficient, [6] developed from the aerodynamic and dynamic solutions of the revolution body with gyroscopic low and high spin coupled motion. Since Eq. (1) is complex but linear, its solution is given as:

(

)

ξ = K10 eiΦ10 e( 1

λ + iΦ1′ ) s

(

)

+ K 20 eiΦ20 e(

λ2 + iΦ 2′ ) s

+ ξ g . (2)

Each value of the angular spin angles as the frequencies Φ j′ , and damping coefficients λj in homogeneous solution, will vary with the relative magnitudes of the H, P, T and M which could be expressed as the basic function derived from the projectile designed form its aerodynamic, flight dynamic, inertial and all over flight performances.

With an aim to separate conditions of damping abilities of a complex angle of attack expressed by λj, and gyroscopic frequencies effect Φ j′ , the conditions of projectile’s dynamic behavior of inertial axes, are enough precise approximately described in [6], [7] and [14], by assuming that Φ1′Φ 2′ >> λ1λ2 .

This provides using a real solution to be applied and considered in the form: 1 Φ j′ =  P ± P 2 − 4 M  , j = 1, 2,

(3)  2 and damping coefficient separated from joint solution as:

P ( 2T − H )  1 λj = − H  , 2  P 2 − 4 M 

j = 1, 2.

(4)

Real values of both λj and Φ j′ , Eqs. (3) and (4) determine gyroscopic stability criterion in the form:

1 4M = 2 , Sg P

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where, Sg > 1 as the obvious condition, from the Eq. (5), for the real roots in Eq. (3). Using aerodynamic coefficient [6] and [7] these expressions are determined by: I x2 p 2 (6)

Sg = , 2 ρ I y SdV 2 CM α where,

P=

I x pd ⋅ , Iy V

(7)

M = CM* α ry−2 .

(8)

The value of Sg is known as the gyroscopic stability factor. A coupled requirement for the stability is that velocity vector angle of attack has to be damped. This is satisfied by the lim ξ → 0 , which s→∞ requires a necessity that λ1 and λ2 are both negative λj < 0, j = 1, 2. This second condition evolves to the so called dynamic criterion of stability Sd as referencing value in Eq. (4), in the form:

Sd =

2T , H

(9)

with values,

* −2

T = CL*α + CMp α rx ,

* H = CL*α − CD* − CMq + CM* α ry−2 ,

(

(10)

)

(11)

where using aerodynamic properties [1], expression is:

Sd =

(

2 CLα + rx−2CMpα

(

)

CLα − CD − ry−2 CMq + CM α

)

.

(12)

The condition that damping coefficients λj have to be negative, relates to the following inequalities, respectively:

and

H > 0,

(13)

 P 2 ( S d − 1)2   2  < 1.  P − 4 M 

(14)

Eq. (15) describe general criteria of dynamic stability for any axis-symmetric projectile spin or fin equipped. According to [6] to [8], the stability criteria Eqs. (6) and (12) are developed in relation to aerodynamic coefficients and derivatives coupled by inertial and dynamic properties of the body motion.

Eqs. (7), (8), (10) and (11) appears as the conditionally for the aerodynamic behavior of projectile’s forces and moments as the loadings expressed by the Murphy’s coefficients, in the Eq. (1) vs. flight Mach numbers, angle of attack, and the so called derivatives in the changes during flight, [6]. Spin stabilized projectiles during the real flight, change damping coefficients Eq. (4) of characteristic Eq. (2), λ1 and λ2, and also factors of stability, Sg, given by Eqs. (5) and (6), and Sd, given in Eqs. (9) and (12), which is further derived. The calculated data are used in changes of stability criteria estimations at the expected muzzle distances after firing from the cannon barrel, [13].

For AA cannon projectile of small caliber this spin stabilized behavior vs. flight Mach number will be considered further as a result of experimental testing of measured aerodynamic coefficients and appropriate semi empirical and theoretical data in the stability criteria Eqs. (6) and (12). The aim is to discover influence of the longitudinal position of lateral aerodynamic Magnus force over derivative of Magnus moment coefficient CMpα, on the spin stabilizing factors, which changes its values vs. flight Mach number from high supersonic to the high subsonic values.

Considerations have been made using the condition in Eqs. (6) and (12), by the complex simulation in redesigned basic software showed in [8], [11] and [13].

3 BASE EXPERIMENTAL EQUIPMENT AND TESTING MODEL SET UP The base experimental equipment used for aerodynamic simulation was the three-sonic wind tunnel test facility T-38, [15]. The tunnel is a blow down pressurized type with a 1.5×1.5 m square test section, aimed for subsonic and supersonic tests, [15]. The tunnel was fully equipped by appropriate equipment to simulate flight flow conditions.

Mach number can be set and regulated to within 0.5% of the required value. Total pressure in the test is within 1.1×105 to 15×105 Pa regulated to 0.3% errors of real flight conditions. Run times are in the range 6 to 60 s, depending on Mach number and total pressure.

The facility supports, step-by-step model movement

These Eqs. (13) and (14) coupled with Eq. (5) gyroscopic conditions Sg > 1, finally give stability expression inequality as: 1 < Sd ( 2 − Sd ) .

(15)

Sg 396 Milinović, M. – Jerković, D. – Jeremić, O. – Kovač, M.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 394-402

and continuous movement of model (“sweep mode”) during the measurements.

Simulation and experimentally tested model of projectile in the tunnel is shown on the Fig. 1, [13]. Characteristic values of mass and dimensions, approximately, corresponds to the AA cannon 40 mm HE unguided projectile, Table 1. The model is supported in the test section by a tail sting mounted on a pitch simulation mechanism by which desired aerodynamic angle can be achieved.

Fig. 1. Model of spin stabilized projectile Table 1. Model of projectile [13] Parameter Symbol, unit Value Reference diameter (cal) d [mm] 40 Total length l [-] ~ 5* Nose length l1 [-] ~ 2.5* Ogive radius Ro [-] ~ 20* Boat tail length l3 [-] ~ 0.5* Center of mass xCG [-] ~ 3.3* Mass of projectile m [kg] ~1.0 Axial inertia moment Ix [kg m2] ~2.1∙10-4 Transversal inertia moment Iy [kg m2] ~2.3∙10-3 * relative values as number of reference diameter (caliber)

Tests on the model were performed in the Mach number range from 0.2 to 3.0 (14 different values of Mach number). The simulated total angles of attack αt, redefined to the angle of attack in vertical plane, α, (pitch angle, as a good approximation to the total yaw angle, pp. 33, [6]), were in the interval, –10 to +10°, [12] and [13]. Test conditions were given in Table 2.

Aerodynamic forces and moments of the model were measured by ABLE 1.00 MKXXIIIA internal sixcomponent strain gauge balance, [13] and [15]. The nominal load range of the balance was 2800 N for normal, 620 N for side forces, 134 N for axial force, 145 Nm for pitching, 26 Nm for yawing moment and 17 Nm, for static spin damping moment; the accuracy was approximately 0.25% F.S. for each component.

Instrumentation and data recording were performed after each run using the standard T38-APS software [15] in several stages, i.e.: Data acquisition system interfacing and signal normalization; Determination of flow parameters in the test section of the wind tunnel;

Determination of the model position (orientation) is relative to test section and airflow. Determination of non-dimensional aerodynamic coefficients of forces and moments for each stage has been performed by appropriate tunnel tests, different software modules, [17].

Table 2. Test conditions [13] Parameter Symbol, unit Value static pressure ps [Pa] 0.2×105 to 2.2×105 stagnation pressure p0 [Pa] 2.3×105 to 6×105* atm. temperature Tatm [K] ≈ 280 Mach number Ma [-] 0.2 to 3 Re number Re [-] 0.5×106 to 2×106 angle of attack (pitch) α [°] –10 to 10 * for all Mach numbers was 2.3·105 Pa, since for Ma = 2.5, p0 =4 ·105 Pa and Ma = 3, p0 = 6·105 Pa.

4 EXPERIMENTAL RESULTS AND SPIN STABILIZED MODELING 4.1 Aerodynamic Coefficients and Derivatives The characteristic functions of aerodynamic coefficients in relation to the flight Mach numbers and angles of attack α, measured in the author’s testing, [13] in the wind tunnel is presented in Figs.

2 to 5, and Fig. 6 represents additional data supposed from [14]. The influenced aerodynamic coefficients tested on the projectile model are aerodynamic coefficient of drag force, Fig. 2, derivative of lift force coefficient presented in Fig. 3, derivative of pitching moment coefficient given in Fig. 4, and all vs. flight Mach number. Flight Mach numbers were corresponding to the projectile flight velocities on the modeling trajectories. Aerodynamic prediction or calculations of coefficients and derivatives are determined with two semi-empirical methods: ADK0 for zero angle drag coefficient and ADK1 for others, [13]. Research was developed according to [11] and [16] to [18]. Data of these predictions for appropriate aerodynamic coefficients are also presented in the same figures and compared with the above mentioned experimental values. Aerodynamic coefficients vs. side slip component of total yaw angle β, was not tested experimentally and further considerations took these effects in integral yaw angle, by semi-empirical predictions denoted as ADK1 in the previously mentioned references. Measurements of the so called dynamic derivatives of pitch damp coefficient in wind tunnel facilities require complex and expensive testing equipment, and improvement of the test model design, which were not used in these experiments.

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0.5

CD [-]

0.4 0.3 0.2

stability of projectiles if the force lateral position along longitudinal axes is not well known, or vary vs. flight Mach numbers changes. Flight Mach numbers and other data are changed on the simulated trajectory by the six degrees of freedom software (6DOF) [6], [8], [11] and [13] modeling.

8

2 exp.α=0

0 0

exp. α=+10o exp. α=-10o ADK0 α=0

o

1

1.5 Ma [-]

2

2.5

1.5 Ma [-]

2

2.5

3

exp.sim.

ADK1

-10

3 CMα. + CMq [-]

0.5

-8 -6 -4

exp.

ADK1

4 CLα [-]

1

-12

5

-2 0

3

1.05

0.5

1

1.5 Ma [-]

2

2.5

3

Fig. 5. Predicted values (ADK1) and simulated experimental values (exp.sim.) of dynamic derivative of pitch damping moment

2

1.5

1 1

1.5 Ma [-]

2

2.5

3

The derivative of Magnus moment coefficient, CMpα, which could not be simulated by the wind tunnel was estimated by calculations from the approximated model ADK1, [13] according to the developed estimations in [6], [7] and [14], Fig. 6. Variations are accepted based on data in [6], [7], [11] and [14]. It was the base challenge in estimation because Magnus force effects influenced the stability similarly as any other lateral force and is composed of flight Mach number effect and spin peripheral velocity designed in the stream flow. This aerodynamic loading coefficient based on the relative small values of real Magnus forces could make undetermined problems to the

calc.det. calc.undet. calc.det.2 calc.undet.2

1 CMpα [-]

0.5

Fig. 3. Predicted values (ADK1) and experimental values (exp.) of derivative of lift force coefficient

398

0.5

Fig. 4. Predicted values (ADK1) and experimental values (exp.) of derivative of pitching moment coefficient

Fig. 2. Predicted values (ADK0) and experimental values (exp.) of drag coefficients

0 0

4

o

0.1 0 0

exp.

ADK1

6 CMα [-]

Experiments of pitch derivatives, vs. flight Mach numbers are approximately determined in the tunnel test simulations using the test model pitch motion, with threshold ability of angular rate in sweep-mode as was 2 degrees per second, [12] and [13]. Values of derivatives of aerodynamic coefficient CMq+ CM α , realized in these experiments are presented in Fig. 5, by dot-points curve realized in the singular flight test runs, vs. 14 values of simulated flight Mach numbers.

A comparison of these values with the data calculated

by ADK1 prediction is also presented in the same figure.

0.5

0 0.5

1

1.5

Ma [-]

2

2.5

3

Fig. 6. Predicted values (ADK1) of derivative of Magnus moment coefficient [14]

The flight conditions are given in Table 3.

Aerodynamic data have been estimated by ADK0, ADK1 and presented from experimental tests.The estimated main derivatives were assumed as the challenge for sensitivity tests of the so called stability vs. flight Mach number, represented velocities on any type of trajectory.

Milinović, M. – Jerković, D. – Jeremić, O. – Kovač, M.

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Table 3. Flight simulation condition [13] Parameter pressure temperature muzzle velocity x component of muzzle angular velocity – spin y component of muzzle angular velocity z component of muzzle angular velocity

Symbol, unit pa [Pa] Ta [K] V [m/s]

Value 1.013 105 288.13 985

p [s-1]

6300

q [s-1] r [s-1]

1.0 ** 7.7 ** Table range angle (gun elevation) θ0 [°] 5 to 20 ** according to the research of the initial fire disturbing conditions, [11] and [13]

4.2 Spin Stability Parameters Modeling Qualitative evaluation of projectile stability is determined through an analysis of the simulated data using software 6DOF, [11] and [13], expressed in the following: • absolute values of total angle of attack |αt| vs. time, Fig. 7, which corresponds to the solution of |ξ| in Eq. (2), with zero initial ξg, • damping behavior λ1,2, of high and law spin of complex |ξ| module, vs. stability factors relation Figs. 8a and b, all vs. flight Mach number, • gyroscopic stability factor Sg and criteria relation, Fig. 9, • spin angular velocity damping p, Fig. 10, • dynamic stability factor Sd and criteria, Figs. 11 and 12, • total stability criteria Fig. 13.

2.5

calc. exp.

|αt | [o]

2 1.5 1 0.5 0 0

0.05

0.1

0.15

0.2 t [s]

0.25

0.3

0.35

0.4

Fig. 7. Absolute simulated angle of attack on the initial part of trajectory

Two groups of aerodynamic data in flight projectile stability modeling are used, as well as calculated data, (ADK1) denoted in Figs. 8 to 13, as the (calc.) and experimental aerodynamic data used from Figs. 2 to 6, composed in the matrix form adapted for the software, and denoted as the (exp.) roots simulations. Experimental rooted data, of αt,

corresponded to the tunnel measured values vs. angles of attack α.

Complex yaw simulations taken from the calculated data and with a total yaw angle αt, composed from vertical (pitch) angle of attack α are simulated to prove the damping effect of velocity direction to the projectile body, which was preliminarily designed by simulation without derivative of Magnus moment coefficient, which means Magnus force point is in the center of mass. Representative damping quality should be exposed at the very beginning of flight within less than half a second, Fig. 7. These influences caused by Murphy’s coefficient H were dominant aerodynamic derivatives calculated estimations and experiments shown in Fig. 5, as the summary dynamic derivatives of coefficient CMq+ CM α , in both, supersonic and subsonic flight Mach numbers, expressed deviations of more than 30 percent for calculated and experimental data. This causes a strong influence on Eq. (11), in the simulation done using static tunnel test data, which was performed by inappropriate derivative measurements. Differences of experimental and calculated data from the initial flight Mach numbers of about 3 to 1.5, are caused in the derivative of pitch damp moment coefficient CMα, Fig. 4, which strongly influenced Sg estimations by calculated and experimental data, Fig. 9. This was significantly exposed for the high initial flight Mach numbers. Approval is shown in Fig. 9 where both gyro stability curves factors and criteria of the calculated and experimental roots make a crossing in the Mach number of 1.5 values. This is in correlation to the values of Fig. 4.

Other related influences on the differences of the angle like the Magnus force and their lateral position along projectile longitudinal axis, affected the side-slip component β in the total yaw angle αt were not considered but were performed through influencing estimations in the stability factors and damping performances in the gyro stabilization.

The angle damping behavior vs. flight Mach numbers, Fig. 7 correlated with the measurement in flight tunnel tests and calculated data with the derivative of Magnus moment coefficient CMpα, Fig. 6, influences are presented in Fig. 8b, expresses negative and 8a, one negative and one positive values of damping coefficients Eq. (4). These data have shown disastrous influencing of derivative of Magnus moment coefficient CMpα, which was tested, using Fig. 6 values by 100% variations, keeping the same other conditions in the stability tests. This means more an unknown position of Magnus force along projectile axis than their intensity values. The

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damping stability coefficients [-]

0.5 x 10

-4

6500 6000

0

5500

-0.5 -1 -1.5

λ2 (calc)

-2 -2.5

damping stability coefficients [-]

-0.5 x 10

1

1.5

Ma [-]

2

3500

λ2 (exp)

3000

-1.5

2

2.5

gyroscopic stability factor [-]

Ma [-] b) Fig. 8. Damping coefficients vs. Mach number; a) for full value of derivative of Magnus moment coefficient, b) for half value of derivative of Magnus moment coefficient

b)

3

a)

Sg (calc)

6

Sg (exp)

5 4 3 2

gyroscopic stability criteria [-]

a)

7

b) 1

1.5

0.6

Ma [-]

2

2.5

3

0.5 0.4 0.3 1/Sg (calc)

0.2 0.1 0.5

1/Sg (exp) 1

1.5

Ma [-]

2

2.5

3

Fig. 9. Gyroscopic stability relation vs. Mach number; a) gyroscopic stability factor, b) gyroscopic stability criteria

differences between experimental and the calculated data vanished by decreasing this derivative vs. Mach number distribution, Fig. 8b. This effect is caused by coupling with estimations of H, Murphy’s coefficient, Eq. (10), which remains positive values, Eq. (13), but vary, making influences on the λ1,2, more on the high 400

(6) calc. θ0=15o 1

1.5

Ma [-]

2

2.5

3

Sd(2-Sd ) (calc) (CMpα )

Sd(2-Sd ) (exp) (CMpα )

1 0 -1 -2 0.5

1

1.5

Ma [-]

2

2 dynamic stability criteria [-]

1.5

dynamic stability criteria [-]

λ2 (exp) (CMpα/2)

1

(5) calc. θ0=10o

(3)

(6)

2

λ1 (exp) (CMpα /2)

-2 0.5

(4) calc. θ0=5o

(2)

Fig. 10. Angular spin velocity vs. Mach number

λ1 (calc) (CMpα /2) λ2 (calc) (CMpα /2)

1 0.5

(5)

2000 0.5

3

(3) exp. θ0=15o

(1)

-4

-1

(2) exp. θ0=10o

(4)

4000

λ1 (exp)

2.5

(1) exp. θ0=5o

4500

2500

-3 0.5

a)

p [s-1]

5000

λ1 (calc)

2.5

3

Sd(2-Sd ) (calc) (CMpα /2) Sd(2-Sd ) (exp) (CMpα /2)

1 0 -1 -2 0.5

1

1.5

Ma [-]

2

2.5

3

Fig. 11. Dynamic stability relation criteria vs. Mach number; a) for full value of derivative of Magnus moment coefficient, b) for half value of derivative of Magnus moment coefficient

frequency damping coefficient λ1 then on the λ2, low frequency damping coefficient, both expressed in the in Eq. (4).

Gyroscopic stability factor determined by the changes of flight Mach number and the data of the projectile model are presented in Fig. 9 demonstrates flight gyro-stability factor as a relation of Eq. (6) vs.

Mach numbers not violated by the derivatives.

The spin velocity, projectile performances are taken in both data types of simulations representative trajectory with equal values vs. Mach number, represented in Fig. 10, and corresponding with projectile model data in Tables 1 and 3.

Changes of spin were not tested experimentally.

The most significant influences of the derivative of Magnus moment coefficient CMpα, Fig. 6, were

Milinović, M. – Jerković, D. – Jeremić, O. – Kovač, M.

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exposed as disastrous on the estimated calculations of dynamic stability factors. In the presented Figs. 11 and 12, the condition of dynamic stability Eq. (15), and stability factor given by Eq. (12) with Magnus moment derivative influences were tested. Influencing of the derivative of Magnus moment coefficient CMpα, which varied 100% in Fig. 6, making the stability of the dynamic factor bigger than 2 thus, making Eq. (15) negative, Fig. 12, and violating stability. Double less values of CMpα vs. flight Mach numbers rearranged the stability of dynamic factors, but making neutral stability approximately. Effects are related to the values of H also by modestly reliable data, taken as the sum of derivatives CMq+ CM α . The sum is shown as influence on the dynamic stability in Fig. 12, with respectable differences between the simulated stability criteria in Eq. (12), with experimental and calculated data vs. Mach number. Values are exposed as the coupled with CLα influences and the above mentioned derivatives.

dynamic stability factor [-]

4.5

(1) Sd (calc) (CMpα )

4

AD Manner of AD parameter parameter increasing CD0 decreasing

increasing CLα decreasing

(3) Sd (calc) (CMpα /2)

3

(4) Sd (exp)(CMpα /2)

2.5

CMq+

CM α

2 1.5

1

1.5

Ma [-]

2

2.5

3

Fig. 12. Influences of derivative of Magnus moment coefficient on dynamic stability factor (5)

1

(6)

0 (4)

-1

(1) 1/Sg (calc)

(3)

(2) 1/Sg (exp)

(3) Sd(2-Sd) (calc)

(2)

-2

(4) Sd(2-Sd) (exp)

(1)

(5) Sd(2-Sd) (calc)(CMpα /2)

-3 0.5

increasing decreasing increasing decreasing increasing

1 0.5 0.5

stability criteria [-]

Table 4. Approximate estimations of aerodynamic parameters’ influences on stability parameters [13]

CMα

(2) Sd (exp)(CMpα )

3.5

denoted expected total stability of projectile in the flight. The coupled effect in Fig. 13 proves that the dominant role of the estimated positive values CMpα of about 0.8 to 0.4, in supersonic and subsonic flight has a negative effect on the projectile flight stability.

(6) Sd(2-Sd) (exp)(CMpα /2) 1

1.5

Ma [-]

2

2.5

3

Fig. 13. Total stability factors equation influences for full and half derivative of Magnus moment coefficient vs. Mach number

Dynamic stability factor Sd and gyroscopic stability factor Sg related by Eq. (15) are presented in Fig. 13 as the final value of stability testing influences vs. Mach number tests and simulations. The main differences of the experimental and calculated data

CMpα decreasing

Stability parameter λ2 1/Sg Sd(2 – Sd) p λ2 1/Sg Sd(2 – Sd) p λ2 Sd(2 – Sd) λ2 Sd(2 – Sd) 1/Sg 1/Sg λ1 Sd(2 – Sd) λ1 Sd(2 – Sd) λ 1, λ 2 Sd(2 – Sd) λ 1, λ 2 Sd(2 – Sd)

Sensitivity of stability parameter increase to 20% increase to 20% increase to 5% decrease 3 to 8% decrease to 20% decrease to 20% decrease to 5% increase 3 to 8% increase to 20% increase to 5% decrease to 20% decrease to 6% increase to 15% decrease to 15% decrease to 30% decrease 2.5 to 7% increase to 30% increase to 8% increase to 30% increase to 25% increase to 30% increase to 25%

These data correspond with [13] but do not fully correspond with [14], and are directed to general conclusions in [6], which are that Magnus moment effect could be expected to be suspicious if it is taken from the data which are not proved by real measurements which are missed in the published data. The paper confirms estimations of instability boundaries and area of main derivative coupling influenced on the flight. Lateral force in the center of gravity proves determination of the stable flight. An Increase of lateral moment derivatives caused by a variation of the force center along the projectile axis is not suggested. Sensitivity of stability factors tested in [13] and in this paper is presented in Table 4.

5 CONCLUSION The stability of AA gun projectile model is affected by aerodynamic coefficients and derivatives through their steady state testing data. The test performed by

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an approximately real designed model of projectile was used, and the obtained measurements are valid but not enough for the full reliable estimations of flight stability. The trait of the change of the based calculated values of aerodynamic coefficients coincides with the experimental results of aerodynamic coefficients but does not satisfy the required conclusions about the stability without derivative measurements. A comparative calculation model of coefficient estimations is tested to prove possible indeterminations which could appear as significant, but were not present in the measurement on the tunnel tests at approximately steady state conditions. Further research of ammunition correction functions could be possible for preliminary consideration by simulated stability methodology of lateral forces required in correction by the method of coefficient derivatives shown in this paper.

Damping efficiency of projectile initial magnitude of angle velocity vector αt (total yaw angle) is about 0.4 seconds after launching, which corresponds to the expected if lateral force is in the center of mass.

Also, sensitivity tests give satisfied frame values of gyroscopic stability and dynamic stability influences for the approximated values of Magnus moments and other similar disturbances representatively arranged in the coefficient derivatives values. Further research should comprise of simulations and a test to develop the best way for ammunition guidance considerations based on the behavior of the main projectile axes and velocity vector during flight. Further dynamic testing of aerodynamic derivatives requires appropriate tunnel facility including equipment for a good simulation of the angular motion for ammunition models tests.

6 AKNOWLEDGMENT The results presented in this paper are made within project No III47029 financed by Ministry of Science and Technology Development of the Republic of Serbia.

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[11] Regodić, D. (2003). Exercises in exterior ballistics.

Military academy, Belgrade. (in Serbian) [12] Jerkovic, D., Samardzic, M. (2008). The aerodynamic characteristics determination of classic symmetric projectile. The 5th international symposium about design in mechanical engineering, KOD, p. 275-282.

[13] Jerković, D. (2009). The influence of aerodynamic coefficients on the motion of axis-symmetrical body.

Faculty of technical sciences University of Novi Sad. (in Serbian) [14] Regan, F.J., Schermerhorn, V.L. (1971). Aeroballistic evaluation and computer stability analysis of the US Navy 20-mm general purpose projectile. NOLTR, p.

71-95.

[15] Elfstrom, G.M., Medved, B. (1986). The Yugoslav 1.5 m trisonic blowdown wind tunnel. 14th Aerodynamic Testing Conference. West Palm Beach, AIAA Paper 8624726, p. 89-95.

[16] Krasnov, N.F. (1985). Aerodynamics 1 – Fundamentals of Theory. Mir Publishers, Moscow.

[17] Krasnov, N.F. (1985). Aerodynamics 2 – Methods of Aerodynamic Calculations. Mir Publishers, Moscow.

[18] Janković, S. (1979). Aerodynamics of projectiles, Faculty of mechanical engineering, Belgrade (in Serbian) [19] McCoy, R.L. (1985). Aerodynamic and flight dynamic characteristics of the new family of 5.56 mm NATO ammunition. Memorandum report BRL-MR-3476, US Army Ballistic Research Laboratory, Aberdeen Proving Ground, Maryland.

Milinović, M. – Jerković, D. – Jeremić, O. – Kovač, M.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 403-410 DOI:10.5545/sv-jme.2012.335

Paper received: 2011-12-20, paper accepted: 2012-03-21 © 2012 Journal of Mechanical Engineering. All rights reserved.

A Model for Shaped Charge Warhead Design

Jaramaz, S. – Micković, D. – Elek, P. – Jaramaz, D. – Micković, D. Slobodan Jaramaz1 – Dejan Micković1,* – Predrag Elek1 – Dragana Jaramaz2 – Dušan Micković1 1 University of Belgrade, Faculty of Mechanical Engineering, Serbia 2University UNION-Nikola Tesla, Faculty of Civil Management, Serbia A model for shaped charge warhead design was developed. The model is incorporated in the computer code - CUMUL. The code includes detonation wave profile estimation, liner collapse, arrival of collapsed liner to the centerline of shaped charge, jet creation and jet breakup.

The penetration phenomena are discussed and governing equations are presented. Two cases dealing with the target type are included: homogenous and non-homogeneous targets. For the purpose of verifying CUMUL, a set of 20 specimens of shaped charges was tested.

The tests were directed to investigate the effect of cone apex angle and stand-off distance on the performance of shaped charge. From the comparison between experiments and CUMUL results, it was concluded that CUMUL program shows a good agreement with the experiments.

That enables it to be a powerful tool for shaped charge warhead design.

Keywords: shaped charge warhead, shaped charge jet, warhead design, computer code, penetration

0 INTRODUCTION Shaped charges are extremely useful when an intense, localized force is required for the purpose of piercing a barrier. The main application is in the military arena, for high explosive antitank (HEAT) rounds including hand-held (bazooka type) rounds, gun-launched rounds (e.g., rifle grenades), cannon-launched rounds, and various bombs. The targets are armors, bunkers, concrete or geological fortifications, and vehicles [1] and [2].

The shaped charge was analysed using an analytical approach for preliminary analysis and parametric studies to determine an approximate design that could satisfy technical requirements. For this purpose we developed models for the following phases: a) estimation of explosive properties, b) detonation wave properties and profile, c) calculation of liner driven velocity, d) calculation of liner collapse velocity and angle, e) jet length determination, f) estimation of target penetration. These models are included in CUMUL computer code. CUMUL program calculations are compared with experimental results that include the study of liner apex angle and stand-off distance influence on the penetration of 64 mm anti-tank rocket with shaped charge.

1 STRUCTURE OF CUMUL PROGRAM The main outline and different approaches adopted in CUMUL are shown in block diagram in Fig. 1. Performing the shaped charge design phases by utilizing the mostly known approaches, make CUMUL a very powerful design tool. In addition, it also provides the designer with a great chance to have a wide range of calculated results which indicate the expected performance for the designed shaped charge.

1.1 Input Data Input data needed for running CUMUL can be classified as follows: • explosive input data, • shaped charge liner shape and dimensions, • target data, • options for approaches to be used for calculations.

1.2 Explosive Properties Determination The explosive properties such as Chapman-Jouguet pressure, detonation velocity and Gurney constant are calculated by the use of empirical equations. The explosive name or names if it is a mixture, densities and percentage are given in the input file. Another data base file contains basic characteristics of 28 explosives.

1.3 Estimation of Detonation Wave Profile Determination of detonation wave attack angle and jet mass calculations are fully depended on the liner shape used. The model of logarithmic spiral is used as a detonation profile technique. Due to the variety of liner shapes, separated subroutines were created, so each liner shape has its own subroutine. There are four subroutines for four different liner shapes: (1) conical, (2) parabolic, (3) biconic, (4) Gaussian.

1.4 Evaluation of Initial Driven Liner Velocity When the detonation wave arrives at the liner, the liner element will accelerate to an initial velocity V0.

In seeking all the approved ideas for this phase, CUMUL provides four approaches for V0 calculations: 1. Asymmetric sandwich.

*Corr. Author’s Address: University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11000 Belgrade, Serbia, dmickovic@mas.bg.ac.rs

403

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 403-410

Fig. 1. Block diagram for CUMUL program

 M N ( X n − X s )2 + = + X s2 2 E  C C

V0

3 1 X s  ( X n − X s )   + 1 +  3 X n  X s3  

where: 2E M C N Xm Xn Xs

−1 2

,

(1)

where Rm radial location of liner surface (Fig. 2) Rn radial location of confinement surface Rs Lagrangian radial position of an assumed stationary surface:

Gurney constant, liner mass per unit area, explosive charge mass per unit area, confinement mass per unit area, location of liner surface, location of confinement surface, location of stationary surface: X s = X n (1 2 + N C ) ( M C + N C + 1) .

3. Chanteret formula [1]:

404

−1 2

.

  N 3β + 1  A M β +3  =  A2  + + − +  2 E   C 6β + 6  3 C 6β + 6 

V0

where:

1 ( Rs − Rm ) ( 3Rm + Rs ) + Rn2 − Rm2 6

1 ( Rn − Rs ) ( 3Rn + Rs )  +  6 ( Rn2 − Rm2 ) ( Rs − Rm )2  

 M 1  +   C 6 

−1 2

,

(3)

4. Hirsch formula [2]:

 M N ( Rn − Rs )2 V0 = + + 2 2 E  C C ( Rs − Rm )

3

 R 2 − Rm2 =  n2 2 2 E  Rs − Rm

V0

2. Gurney formula for imploding cylinder

+

  N M  Rs3 + 3Rs ( Rn + Rm )  Rn + Rm  + Rm Rn  − C C      2  M N 

−3Rm Rn ( Rn + Rm )  +  +   = 0.  3  C C 

(2)

M β +2 β+ R C 3β + 3 A= , β= n.

N 2β + 1 Rm + C 3β + 3

Jaramaz, S. – Micković, D. – Elek, P. – Jaramaz, D. – Micković, D.

−1 2

, (4)

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 403-410

where the prime indicates differentiation with respect to the Lagrangian liner coordinate x. The symbol τ is time parameter related to the acceleration of the liner.

When the liner element collapses, the driven velocity history is assumed to follow one of the following profiles (Fig. 4):

Fig. 2. Control mass for concentric cylinder liner

1.5 Evaluation of Liner Collapse A diagram of the general charge geometry and liner collapse is shown in Fig. 3. The explosive is detonated at B. As the detonation wave passes P, the liner element originally at P begins to collapse in a direction that makes an angle δ with the normal to the original liner at P. The detonation wave speed D is considered normal to the wave front. However, the velocity with which the wave sweeps the liner is not constant , however, and is given by the formula: D U ( x) = , cos γ

(5)

where γ = γ(x) is the angle between the normal to the detonation wave at P and the tangent to the liner at P (see Fig. 3).

Fig. 3. Charge geometry and collapse

The projection angle for the unsteady case is:

δ=

V0 1 ' 1 ' − τV + τ V , 2D 2 4

(6)

Fig. 4. Liner collapse velocity profile; a) instantaneous acceleration, b) constant acceleration, c) exponential acceleration

The liner elements in the classical theory were assumed to reach collapse velocity instantaneously (Vc = V0). The first level of refinement assumes that velocity increases linearly over a short period until it reaches final velocity V0 or collapses on the axis. The velocity history that assumes an exponential form was proposed in [5]. The time base used is t = 0 when the detonation wave is at x = 0 on the liner. T = T(x) is the time when the detonation wave reaches the element x on the liner.

The three velocity profiles were involved in CUMUL. For example, for each initial driven liner velocity (i.e. asymmetric sandwich, Gurney, Chanteret or Hirsch), the three categories are applied to cover all the assumed possibilities that describe the way of movementand traveling path, which the liner element had followed [6].

In order to develop the contour of the collapsing liner we write the coordinates of general point P' in Fig. 3, as it collapses at time t to the point M. The coordinates of point M are:

A Model for Shaped Charge Warhead Design

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 403-410

z = x + l ( x, t ) sin (α + δ ) ,

(7)

r = R ( x ) − l ( x, t ) cos (α + δ ) ,

(8)

where z is the axial coordinate, r is the radial coordinate, R is the original liner radius, and l(x,t) is the distance the element has travelled from P' to M. The angle of impact of the liner with the axis is given by:

tan β =

R' −

∂l ( x, tc ) cos (α + δ ) ∂x

the initial jet length, mass, diameter, arrival time and arrival velocity are calculated. On the other hand, the same procedure is applied to calculate the slug properties as well, but, because the slug part does not contribute in penetration phenomena, it is coming out of the picture of interest.

In order to trace the location of the jet elements and study their stretching after formation the coordinate system conventions shown in Fig. 5 are adopted.

+ ∂l ( x, tc ) sin (α + δ ) + R (α + δ ) 1+ ∂x R (α + δ ) tan (α + δ ) , (9) + ∂l ( x, tc ) 1+ sin (α + δ ) + R (α + δ ) ∂x

where tc = tc(x) is the time of impact and the prime indicates differentiation with respect to x. The derivative ∂l / ∂x is evaluated at a proper impact time.

Once β has been calculated the velocities of each element of jet and slug are calculated from:

Vj =

Vc

β  cos  α + δ −  , β 2  sin 2 Vc

β  sin  α + δ −  , Vj = β 2  cos 2

(10)

(11)

A ring element of the liner of mass dm splits into an element of jet of mass dmj and an element of slug dms. These masses are defined by:

dm j

β , 2

(12)

dms β = cos 2 .

2 dm

(13)

dm

= sin 2

Lagrangian coordinate x defines the original position of the liner elements along the axis. The position coordinate in the jet is measured from the original position of the liner apex and is designated as ξ(x,t).The position of an element at the moment it just reaches the axis is denoted by z ( x) . From the basic collapse geometry, (Fig. 3), the position is given by:

where Vc = Vc(x,tc).

Fig. 5. Description of coordinates

z ( x ) = x + R tan (α + δ ) .

(14)

At any time t > tc a portion of the element originally at x will be in the jet. Assuming that each element of the jet travels at a constant velocity Vj(x) immediately after it is formed, the position of the x element at time t is:

ξ ( x, t ) = z + ( t − tc )V j , t ≥ tc .

(15)

The one-dimensional extension of the jet elements may now be defined in the following manner.

Consider two points x1 and x2 on the liner separated by a distance Dx as shown in Fig. 6.

1.6 Evaluation of Jet Forming and Stretching During this phase, the first step is to consider the jet forming case, that i, at the moment when the collapsed liner elements arrive to center line of shaped charge.

This consideration does not include stretching and particulation of the jet. At the moment of jet formation 406

Fig. 6. Extension of a jet element

During the collapse process the point x1 reaches the axis and then proceeds to jet along the axis.

Jaramaz, S. – Micković, D. – Elek, P. – Jaramaz, D. – Micković, D.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 403-410

Meanwhile, x2 has begun to collapse and reaches the axis at time t0 = tc(x2). At this moment t0, jetting material originally at x1 is located at ξ(x1,t0) and x2 has just reached the axis and is located at ξ(x2,t0). At some arbitrary later time t, their locations are ξ(x1,t) and ξ(x2,t), respectively. One-dimensional jet extension is defined as the ratio of the increase in length of a jet element to its length when first formed:

E = lim x2 → x1

∆ξ − ∆ξ 0 = ∆ξ 0

∂ξ  ∂ξ =  ( x1 , t ) ( x1 , t0 ) − 1, ∂x   ∂x

(16) Fig. 7. Typical jet velocity distribution curve

where t0 = tc(x1).

The second step is to consider jet stretching and particulation phenomena. The main outlines of these phenomena can be summarized as following: A. Jet Tip Calculation. It is a start point for jet forming calculation. Jet tip mass, length, velocity and number of liner elements involved in jet tip creation are founded, keeping in mind, that, the tip is not exposed to stretching [7].

In many cases the liner has a region where the elements do not reach the final collapse velocity. In this region, close to the charge axis, an element with jetting velocity Vj1 may be followed by an element with greater jetting velocity (Vj2>Vj1). This inverse velocity profile usually continues throughout this region and the mass piles up forming the jet tip. Each element is considered to impact until the first jetting element whose velocity is less than the velocity of the combined tip projectile. Then, conventional jetting ensures. Assuming a pefectly plastic impact of elements the conservation of linear momentum leads to the following expression: xtip

V j ( xtip ) =

∫ Vj ( x) 0

xtip

∫ 0

dm j

dm j dx

dx

dx ,

(17)

dx

where V j is velocity of the combined tip particle, and dmj/dx mass of jet element per unit lenght of original cone.

Eq. (17) is integrated step by step until a point xtip is found such that:

V j ( xtip ) ≤ V j ( xtip ) .

stops and where normal jetting begins. This value of xtip is presented in Fig. 7.

(18)

The value of xtip is considered as the point on the liner that distinguishes where the formation of the tip

B. Breaking up Time. Breaking up time is the maximum time spent in jet stretching operation before jet particulating take place. CUMUL provides two formulas for estimating the possible breaking up time for shaped charge [8] to [10].

C. Jet Stretching. After finding break up time, the maximum jet stretching is calculated, and therefore, the final or the total jet length is founded [11].

1.7 Penetration Referring to Fig. 1, it can be seen that the penetration phase is created according to the following classification: 1.7.1 Homogenous Target When the target consists of one material it is called a homogenous target. In this case, there are two possible ways of calculations: a) No virtual origin is applied. In this case the stand off distance is taken as it is provided by the user. b) Applying virtual origin approach [12]. A virtual origin is an important issue for determining the stand off distance. By finding the location of virtual origin, the stand off distance can be easily achieved by simple addition operation.

The penetration value for both cases can be calculated by the following techniques (this can be decided by the user) [13]: 1. density law formula (DL), 2. minimum jet velocity (Vmin), 3. minimum penetration velocity (Umin).

1. For a jet of constant velocity, assuming that the penetration stops when the jet length is consumed, the penetration is given by the density law formula:

A Model for Shaped Charge Warhead Design

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 403-410

ρj

P = Lj

ρT

,

(19)

where Lj is jet length, ρj liner density, and ρt target density.

2. For a jet of non-uniform velocity distribution, the jet length is not constant but increases with time.

Three cases are considered:

a) Penetration before jet break-up 1   γ V   jtip  P=S  − 1 ,  Vmin    

(20)

where S is stand-off distance, Vjtip jet tip velocity, and Vmin minimum jet velocity capable to penetrate the target material γ = (ρT / ρj)1/2.

In this case S is bounded by:

V 0 < S ≤ Vmin tb  min V  jtip

1

γ  , 

 ρT 2 R  ρT   1− L j 1 − +  2   ρ j ρ jV jtip ρ j      , (23) P=  ρT 2 R  ρT  ρT + 1− − 2   ρ j  ρ j ρ j ρ jV jtip 

where ρt is target density given by ρH / ρj , ρh hydrodynamic density, and R target resistance factor.

2 EXPERIMENTAL WORK AND MODEL VERIFICATION The main aim from the present experimental work is to measure the penetration caused by specified shaped charge. This includes the study of changing cone apex angle and stand off distance on the resulting penetration.

where tb is breaking up time of the jet. b) Jet breaks during penetration

P=

(1 + γ ) (V jtip tb )

1 1+ γ

S

γ 1+ γ

− Vmin tb

γ

− S , (21)

where S is bounded by:

V Vmin tb  min V  jtip

1

γ  < S < V jtip tb . 

c) Jet breaks before reaching the target

(V P=

jtip

− Vmin ) tb

γ

,

Fig. 8. Conical shaped charge (apex angle = 50°)

(22)

for stand-off in the range V jtip tb < S < ∞.

3. Formulae for penetration based on minimum penetration velocity (Umin) are similar to those given for minimum jet velocity (Vmin).

1.7.2 Non-Homogenous Target A non-homogenous target is defined as the target which consists of many layers of different material.

Due to the target non-homogeneity a target resistance 408

factor was defined. By using this factor the expected penetration value can be calculated using the formula [14]:

Two models of shaped charge with conical liner were implemented in experimental work. The first model with apex angle 2α = 50°, second model has an apex angle 2α = 60°. The defined shaped charge having a 64 mm diameter and HMX explosive material was chosen. The two models are shown in Figs. 8 and 9, respectively.

A hard cylindrical paper was used to control the standoff distance. Three steel plates with 300, 10 and 25 mm thickness were used as a target. Three shaped charges with different standoff distance are shown in Fig. 10. A set of 20 conical shaped charges were divided into 4 groups.

Jaramaz, S. – Micković, D. – Elek, P. – Jaramaz, D. – Micković, D.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 403-410

A complete analysis and comparison of the theoretical and experimental results were performed.

Three different acceleration histories were implemented. Penetration results were calculated using density law, minimum jet velocity and minimum penetration velocity approaches. Four approaches for calculating liner collapse velocity were involved.

shown in Table 1. A stand-off distance is expressed in term of charge diameter (d).

Table 1. Penetration results Liner apex angle 50° 60°

experiment Calculation experiment Calculation

Stand off distance [mm] 2.5 d 3d 4d 290 306 320 291 311 340 276 264

Computational results presented in Table 1 were obtained by the CUMUL code with the following approaches: Initial driven liner velocity - Hirsh formula, Liner collapse velocity - Constant acceleration, Jet formation and breakup - Hirsh formula, Penetration - Virtual origin applied,

- Minimum jet velocity.

Fig. 9. Conical shaped charge (apex angle = 60°)

From the computational results of jet penetration concerning the stand-off and cone angle effect, it was found that the minimum jet velocity approach with virtual origin was in an excellent agreement with experimental results. The other two approaches i.e. density law and minimum penetration velocity also gave a reasonable agreement.

3 CONCLUSIONS

Fig. 10. Three typical shaped charges with different standoff distances

A complete analysis and comparison of the theoretical and experimental results were performed.

Three different acceleration histories were implemented. Penetration results were calculated using density law, minimum jet velocity and minimum penetration velocity approaches. Four approaches for calculating liner collapse velocity were involved.

The experimental and computational results of jet penetration in steel target for liner with apex angle 2α = 50° and 2α = 60° at different stand-off distances are

The theoretical model and CUMUL computer code were built to perform the complete analysis for shaped charge design work. It provides a wide range of using all the recently approved techniques which are applied for shaped charge design.

In order to verify the results obtained by CUMUL code, a set of 20 experiments were conducted. Two models with cone angle 50 and 60° were prepared for tests. The results for the two models for different stand-off distances were also performed.

Good agreement of theoretical and experimental results shows the CUMUL program is a powerful tool for a preliminary design of shaped charge and for parametric studies of influence parameters on its performances.

4 ACKNOWLEDGEMENT This research work has been supported by the Ministry of Education and Science of Republic of Serbia, through the project III-47029, which is gratefully acknowledged.

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5 REFERENCES [1] Walters, W. (2008). A Brief History of Shaped Charges.

24th International Symposium in Ballistics, New Orleans, p. 3-10.

[2] Janzon, B., Backofen, J., Brown, R., Cayzac, R., Diederen, A., Giraud, M., Held, M., Horst, A., Thoma, K. (2007). The future of warheads, armour and ballistics. 23rd International Symposium in Ballistics, Tarragona, p. 3-27.

[3] Conner, J.M., Quong, A.A. (1993). Velocity of Explosively Driven Liners. Carleone, J. (ed.), Tactical Missile Warheads, AIAA, progress in Astronautics and Aeronautics, vol. 155, New York.

[4] Hirsh, E. (1986). Simplified and extended gurney formulas for imploding cylinders and spheres.

Propellants, Explosives, Pyrotechnics, vol. 11, p. 6-9, DOI:10.1002/prep.19860110103.

[5] Randers-Person, G. (1976). An improved equation for calculating fragment projection angle. Proceedings of 2nd International Symposium on Ballistics, Daytona Beach.

[6] Hirsh, E., Chou, P.C., Ciccarelli, R.D. (1986). General kinematical solution to the motion of an explosively driven liner. Propellants, Explosives, Pyrotechnics, vol.

11, p. 53-64, DOI:10.1002/prep.19860110205.

410

[7] Carleone, J. (1993). Mechanics of Shaped Charges.

Carleone, J. (ed.), Tactical Missile Warheads, AIAA, progress in Astronautics and Aeronautics, vol. 155, New York.

[8] Chou, P.C, Carleone, J., Karpp, R.R. (1974). Study of shaped charge jet formation and breakup. US Army Ballistic Research Laboratory, BRL-CR-138.

[9] Hirsh, E. (1979). A formula for the shaped charge break-up time. Propellants, Explosives, Pyrotechnics, vol. 4, p. 89-94, DOI:10.1002/prep.19790040502.

[10] Hirsh, E., Backofen, J. (2007). Scaling of the shaped charge jet break-up time. 23rd International Symposium in Ballistics, Tarragona, p. 127-134.

[11] Walters, W.P., Zukas, J.A. (1989). Fundamentals of Shaped Charges. John Wiley & Sons, Inc., New York.

[12] DiPersio, R., Simon, J., Merendino, A. (1965).

Penetration of shaped charge jets into metallic targets.

US Army Ballistic Research Laboratory, BRL-R-1296.

[13] Walters, W.P., Flis, W.J., Chou, P.C. (1988). A survey of shaped charge jet penetration models. International Journal of Impact Engineering, vol. 7, no. 3, p. 307325, DOI:10.1016/0734-743X(88)90032-2.

[14] Segletes, S.B. (1997). Homogenized Penetration Calculations. International Journal of Solids and Structures, vol. 34, no. 1, p. 47-59, DOI:10.1016/00207683(95)00286-3.

Jaramaz, S. – Micković, D. – Elek, P. – Jaramaz, D. – Micković, D.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 411-415 DOI:10.5545/sv-jme.2011.280

Paper received: 2011-12-20, paper accepted: 2012-05-04 © 2012 Journal of Mechanical Engineering. All rights reserved.

The Influence of Part Dimensions and Tolerance Size to Trigger Characteristics Macko, M. – Ilić, S. – Jezdimirović, M. Martin Macko1,* - Slobodan Ilić2 – Mirko Jezdimirović2 1 University of Defence, Czech Republic 2 Defence University, Military Academy, Serbia

This article describes a negative effect of size tolerance on the trigger characteristic. The trigger characteristic is the dependence of trigger force and trigger angle. An invalid trigger characteristic affects the accuracy of shooting and can be changed by not only proper choice of dimensions, but also the location of individual components. The paper shows an example of trigger mechanism that is designed as a Glock type mechanism. The solution for designers of small arms authors suggested the use of software MW. Keywords: dimensions, tolerance, accuracy, trigger mechanism, trigger characteristic

0 INTRODUCTION The problem of production accuracy and precision, as well as the shape and position of movable and immovable integral parts of assemblies and mechanisms is the topic of many papers. There are different approaches to this problem. On the one hand, a number of authors focus on the influential parameters, production of parts surfaces, while, on the other hand, some authors deal with the measurement of the load assemblies and components, and their influence on the overall product design. For example, in [1], the authors focus their attention on the changing axis of the tool position in relation to the surface to be processed by milling. Their target was achieving an increase in milling efficiency (improvement of functional surface properties, increase in milling accuracy, increase in tool durability, decrease in energy load on a machine, and shortening of milling time). Proper selection of monitoring points is of paramount importance for drawing conclusions about the design of products based on the measured parameters, regardless of the size scale. In paper [2], the authors had chosen the strain as the relevant influential parameter to measure. The aim of their study was to determine the forces acting on a foldable bicycle riding during various situations. For this purpose, the test bicycle was equipped with strain gauges connected in full Wheatstone bridges at eight measuring points.

Similar problems are met at the hand arms design.

One of the main characteristics of hand arms is certainly the accuracy. Accuracy of shooting depends on various factors: the position of barrel muzzle during firing, shapes and types of bullets, atmospheric conditions, but especially, trigger mechanism displacements and forces balancing.

The first factor, the position of a muzzle, is directly affected by both, subjective, as well as objective parameters caused by mechanism design.

The subjective parameters are related to the individual user – shooter. The proper aiming and possession of arms, especially the motion of the forefinger on the trigger during triggering (Fig. 1) is the most important.

Fig. 1. The influence of forefinger motion on the trigger mechanism; a) usual forefinger position on the trigger, b) forefinger movement and trigger movement are different, c) different forefinger movement and trigger movement causes moment of force M, d) Moment of force M causes muzzle movement

The relation between the trigger mechanism and the shooter is content in fact that forefinger force acts on the trigger, during the process of triggering, changing the position of the barrel muzzle according to the triggering mechanisms internal forces and momentums [3] and [4]. Trigger force is equal to the resistance of the trigger. The value of force triggering

*Corr. Author’s Address: University of Defence, Kounicova 65, 66210 Brno, Czech Republic, martin.macko@unob.cz

411

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 411-415

is usually stated in the specifications of arms only as a (maximum) trigger force. Trigger force causes the movement of the barrel muzzle and the shooter with an adequate reaction, tries to keep the barrel position directed towards the line of sight.

Objective parameters related to the construction of arms parts and mechanisms, their position, dimensions and accuracy of production. The position of the barrel muzzle during the shooting process is under a direct influence of the trigger mechanism characteristics. The trigger characteristic represents dependence of trigger force on the trigger rotation angle. In each moment of the process, the firing trigger force has different values of Fos and direction of Fos . One of the main designer task is to achieve optimal growth of the trigger characteristic and the correct choice of dimensions, positions and tolerances of trigger mechanism parts.

internal displacements, the designer should develop a right form of the trigger mechanism [6].

As an example of an analysis DA trigger mechanism similar mechanism of pistol Glock 17 (Fig. 3) with appropriate dimensions of mechanism parts [7] is taken.

1 STATE OF THE PROBLEM

The trigger characteristic harvesting depends on many parameters. Fig. 4 shows the selected influential parameters (marked in capital letters) on the simulation model of trigger mechanism. Based on Fig. 4 the designer obviously has a vision about points and position to released function, loadings and initial displacements in the process of the triggering.

Also, the main influence parameters are selected as the contact points in the mechanism during triggering which connects the internal mechanism design.

Arms designer should aim to achieve a smooth trigger characteristic, with slight force increasing, without a large rebounding of barrel. Such a change of force has an effect at least on the accuracy of shooting.

Fig. 2 provides an overview of trigger force change and characteristic values of Fos for double action (DA) trigger mechanism, tested in paper [5]. These characteristics are given as an example of values for maximal trigger forces vs. trigger angles.

Fig. 3. Simulated firing mechanism

Fig. 4. Influential parameters on the trigger characteristic Fig. 2. Experimental trigger characteristics

The purpose of trigger mechanism is cocking and the release of impulse mechanism in a desired point of arms initial cup. The release of the impulse mechanism affects the movement of arms because the shooter affects the trigger by the force of the forefinger and hand holding of the arms is not stationary. Through the optimal trigger characteristic with help of smallest 412

This provides the designer with the capability to optimize dimensions and parts positions based on the criteria of trigger force maximum and/or trigger angle maximum. The solution of a simulation model provides a schematic view of the most important forces and the distances (Fig. 5) in the mechanism between parts of the mechanismand the direction of the parts displacements: Fos – trigger force, Fb – reaction between trigger bar and firing pin safety, F2 – firing pin safety force, F3 – firing pin force, F4 –

Macko, M. – Ilić, S. – Jezdimirović, M.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 411-415

trigger bar spring force, Fm – reaction between trigger bar and firing pin, Fz – reaction between trigger bar and the inclined plane, l - trigger bar horizontal displacement, sm - trigger bar vertical displacement equals sz, sbp – firing pin displacement, sc – firing pin safety displacement, φs - trigger angle, γ - trigger bar inclinated plane angle, χ - inclinated plane angle.

Fig. 5. Main forces, angles and displacement of the simulated mechanism

2 SIMULATION TOOL There is various software for tolerance analysis or synthesis [7]: Sigmund is a 3D tolerance analysis software package developed by Varatech and is fully integrated with major packages such as ProEngineer, SolidWorks, and SolidEdge.

MITCalc is designed in Microsoft Excel as an open system. MITCalc contains the design calculation tool: Tolerance analysis of various dimensional chains. The program solves the problem of tolerance analysis and optimization of a dimensional chain using the Worst case, the statistical RSS method, 6 Sigma method and the Monte Carlo.

TASysWorks is a 3D tolerance software package integrated with SolidWorks. It consists of two modules: TASysWorks for tolerance analysis and TASysWorksINTOL for tolerance synthesis in mechanical assemblies. TASysWorks allows four kinds of tolerance analysis: worst-case, RSS, Monte Carlo Simulation, Quadrature Technique and can provide linear and non-linear statistical analysis.

CETOL 6 Sigma is a software package integrated with both Pro/ENGINEER and CATIA V5. It allows users to model-analyze and allocate tolerances based on product performance requirements, while considering manufacturing process capabilities. It can handle three analysis models: derivative-based (Worst-case analysis, RSS analysis) and Monte Carlo simulation.

OptQuest is an optimization software tool that performs uncertainty and tolerance analysis through the process of defining constraints, specifying the objective of the outcome, and setting the requirements.

OptQuest finds the optimal solution through Monte Carlo simulation. For tolerance synthesis the OptQuest works with a statistical distribution of component dimensions (the distribution gallery of OptQuest contains 12 different distributions) and the user enters the cost of components into the spreadsheet.

VarTran is a tolerancing package for tolerance analysis and optimization. It can perform all the standard analysis including statistical tolerancing, worst-case tolerancing, and sensitivity analysis. To optimize product or process performance VarTran provides three methods: maximize Cpk (Process Capability Index), minimize the defective percent and Taguchi loss method.

For the analysis of dimensions, position, tolerance, forces and momentums as well as delays of the trigger mechanism, simulation components are tested by software solution MW [7]. The interface structure of the software package MW is shown in Fig. 6.

Fig. 6. The interface structure of software package MW for the simulation of triggering

3 The results of THE simulation The software solution of a simulation model gives designers the ability to analyze the forces, moments and displacement changes of individual points of the trigger mechanism in the design phase. This ensures an optimal distribution of trigger mechanism parts and a precise definition of the dimensions In the aim to prove software model design which supported the date in Fig. 5 the initial input trigger force vs. angle of triggering is presented similarly to the experimental values in the Fig. 2. This was simulated for a similar mechanism of hand arm Glock 17. The diagram, (Fig. 7), shows the bouncing force

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60

bouncing force peak

Trigger Force [N]

50 40

Fig. 9 represents basic displacement coordinates of mechanism parts which determine main force F3 of arms operation function. Delay trigger angle Dφ orientated instant of releasing firing pin and tolerances field which determines this as threshold for arms rebounding caused by jump of trigger force.

3.5 3 displacement [mm]

peak of triggering force vs. the triggering angle on the mechanism, at the singular value of trigger angle, which is about 18 degrees. This form of characteristic is not welcome because during firing it has a negative influence on the jump of the barrel muzzle. The software simulation done in this paper to solve the causes in the mechanism of triggering determine this force peak as the main problem, which generates rebounding of barrel and arm.

2 1.5 Dϕ

1 0.5

30

0 0

20

5

5

10

15 18 20 Trigger Angle [o]

25

30

Fig. 7. The trigger characteristic for initial values

The basic concept of simulation provides displacement testing and forces vs. dimensions, shown in Fig. 5, and estimations which one is decisionally important for proper functioning and operation. Obvious disturbance is shown in the Fig. 7 absent in Fig. 2 correlated to the input or output force vs. input triggering angle. The input force is the trigger force FOS. The output force of the mechanism is firing pin force F3 (Fig. 5). The relation between these forces vs. trigger angle is shown in Fig. 8. For the fixed values of mechanism parts dimensions, these two forces relation vs. angle are not changed. Also, disturbing jump of trigger force remains on F3 curve.

This orientated that the main influence on the trigger force lays in dimensions and tolerances of input and output coordinates.

15 20 Trigger Angle [o]

25

30

A position of the K-point (Fig. 4) is very important for this type of the trigger mechanism.

Change of x-position K (coordinate system is determined by help of rotation point of the trigger S: x-position point S is 100 mm and y-position point S is 100 mm) allows to provide so called “timing” of firing pin releasing. It means in tolerance field causes the changes of firing pin shift instant and determining of safety, out of function operation affecting. In the Fig. 8 is showed a shape of trigger characteristic (solid curve) for initial dimensions (according to technical drawing) of the simulation while in the Fig. 10 are showed two examples - results of the simulation: the solid curve is for shooter acceptable shape of the trigger characteristic and dashed curve shows wrong shape. The coordinate of x-position K was varied from 117.82 to 117.40 mm. The first result of the simulation is showed in the Fig. 10 for the x-value 117.66 of the K point: solid curve of trigger force does not a jump in the trigger angle of 18 degrees. This is acceptable solution for shooting.

Trigger Force [N]

50 40

parameter K parameters K and Zh

30 20 10 0 0

Fig. 8. Relation of input and output forces vs. trigger angle (F3 dashed curve, F0S solid curve)

414

10

Fig. 9. Changes of displacement vs. trigger angle

10 0 0

Sbp Sc

2.5

5

10

15 18 20 Trigger Angle [o]

25

30

35

Fig. 10. Change of triggering force – variation of the parameters K and Zh

Macko, M. – Ilić, S. – Jezdimirović, M.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 411-415

The second example of the simulation in the Fig. 10 (dashed curve) shows the change of the y - position Zh (x-position of the K-point was kept 117.66 mm from the first example). For change of the y - position Zh from 117.53 to 118.53 mm the impact on the trigger characteristic is too big: the change causes the shift of the firing pin release time (delaying).

It is possible to choose more variations of different parameters in order to find the right shape of the trigger characteristic.

4 CONCLUSION A designer should provide a tolerance analysis or tolerance synthesis in the frame of the preliminary design phase of the mechanisms design [8]. It is possible to solve this problem automatically by various software or by analytical considerations for the main string parameters which determinate the goal function. By using different software packages a designer can achieve a way of quicker and simpler provision of optimal solutions for assemblies and its size tolerances related to the function. Using results of the analytical study achieves a more effective design of the trigger mechanism by reason of observing the condition for acceptable trigger characteristics. Using special software for the simulation of the triggers or other mechanisms it is possible to gain information about all the parameters that influence trigger function.

This means not only size, tolerances, positions but also forces, coefficients of friction, etc. This way takes into account, the so called instant delay of the mechanism, while CAD software products provide only tolerance analysis or synthesis.

Monitoring the changes of individual forces and displacements, which have an impact on a major trigger force, may lead to the conclusion and the profile vs. time of their actions, or timing of all trigger mechanism parts. In this way, it is much easier to

analyze the function of the arms and quickly select all illogical variations of parameters from analysis.

5 ACKNOWLEDGMENT Results presented in this paper have been gathered within project No III 47029 financed by the Ministry of Science and Technology Development Republic of Serbia.

6 REFERENCES [1] Sadílek, M., Čep, R., Budak, I., Soković, M. (2011).

Aspects of using tool axis inclination angle. Strojniški vestnik - Journal of Mechanical Engineering, vol. 57, no. 9, p. 681-688, DOI:10.5545/sv-jme.2010.205.

[2] Pirnat, M., Savšek, Z., Boltežar, M., (2011). Measuring dynamic loads on a foldable city bicycle. Strojniški vestnik - Journal of Mechanical Engineering, vol. 57, no. 1, p. 21-26, DOI:10.5545/sv-jme.2009.149.

[3] Vítek, R., (2009).The generally unbalanced projectile load on the sporting rifle barrel. Proceedings of the 8th WSEAS ICOSSSE, Genova.

[4] Vítek, R., Jedlička, L. (2010). Effect of the accuracy of target range measurement on the accuracy of shooting.

Advances in Military Technology, vol. 5, no. 2, p. 6983.

[5] Macko, M. (1996). Synthesis of the trigger mechanisms according to the trigger characteristics. Proceedings of 1th International Armament Conference, Military University of Technology, Solina, vol. 3, p. 55-60.

[6] Fišer, M., Lipták, P., Procházka, S., Macko, M., Jozefek, M. (2007.) Automatic Weapons. Alexander Dubček University of Trenčín, Trenčín.

[7] Macko, M. (2011). Influence of the size tolerances on the small arms trigger characteristic. Proceeding of OTEH, Belgrade. p. 228-232.

[8] Feng, C-X., Kusiak, A. (2000). Robust tolerance synthesis with the design of experiments approach.

ASME Transactions: Journal of Manufacturing Science and Engineering, vol. 122, no. 3, p. 520-528, DOI:10.1115/1.1285860.

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 416-421 DOI:10.5545/sv-jme.2011.275

Paper received: 2011-12-20, paper accepted: 2012-05-18 © 2012 Journal of Mechanical Engineering. All rights reserved.

Experimental Research on New Grade of Steel Protective Material for Light Armored Vehicles Bernetič, J. – Vuherer, T. – Marčetič, M. – Vuruna, M. Jure Bernetič1,* – Tomaž Vuherer2 – Matjaž Marčetič1 – Mladen Vuruna3 1 Acroni Jesenice, d.o.o., Slovenia 2 University of Maribor, Faculty of Mechanical Engineering, Slovenia 3 University of Defense, Military Academy Belgrade, Serbia

An investigation of new PROTAC 500 armour steel was conducted. Three plates were heat treated to different states. One was quenched, the second and third were quenched and low temperature tempered at 220 and 280 °C for 3 hours. A tensile test, hardness measurements, and an instrumented Charpy test were performed. Metallographic was performed by optical microscopy (OM). Ballistic resistances of all three steel plates were measured. The behaviour of steel was tested using armour piercing projectiles 7.62×39 mm API BZ (former soviet designation for Armor Piercing Incendiary bullet). The best results were obtained in quenched state.

Keywords: armour steel, hardness, instrumented Charpy test, armour piercing projectiles

0 INTRODUCTION

Table 1. Chemical composition of PROTAC 500 steel

The trends of worldwide armour community is currently accelerating efforts to deliver lightweight armour technologies that can defeat armour piercing (AP) projectiles at reduced areal weights and that they are available across a large industrial base [1] to [3]. While many of these programs involve the application of lower density metals, such as aluminium and titanium, the selection of steel alloys is still competitive for many ballistic and structural applications. The ability to produce armour components in both commercial and military operational areas with available equipment and personnel is a major advantage of steel based solutions. To meet these requirements, the worldwide armour community has increased the availability of quenched and tempered armour steels by updating current steel military specifications [4] to [6]. One of those programs is at a steel mill in Acroni Jesenice, Slovenia, where new low heavy weight grade armour steel PROTAC 500, was developed and which is presented in this paper.

1 MATERIAL Three different states of steel were examined. Steel in State A was quenched, steel in State B was quenched and low temperature tempered at 220 °C for 3 hours, and steel in State C was quenched and tempered at 280 °C for 3 hours.

New grade of 8 mm thick steel plate material, developing as PROTAC 500 (chemical composition is in Table 1) sign, prepared by three different thermal treatment states, is used for this research, Table 2.

416

C 0.3

Chemical composition of PROTAC 500 wt.% Si Mn Cr Ni 0.7 1.2 0.8 0.7

Mo 0.35

Fig. 1. Heat treatment; a) of State B, and b) State C

Table 2. States of the testing material PROTAC 500 used in research tests State A

State B

State C

Water quenched

Tempered at 220 °C for 3 hours

Tempered at 280 °C for 3 hours

State A was water quenched. States B and C were quenched and tempered. Heat treatment of steel in state B is shown in Fig. 1a. Steel was heated at 220 °C for 3 hours and cooled down in a furnace. Heat

*Corr. Author’s Address: Acroni, d.o.o., Cesta Borisa Kidriča 44, 4270 Jesenice, Slovenia, jure.bernetic@acroni.si

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 416-421

treatment of steel in state C is shown in Fig. 1b. Steel was heated at 280 °C for 3 hours and cooled down in a furnace.

2 EXPERIMENTAL PROCEDURE AND APPROPRIATE EQUIPMENT Mechanical and instrumented Charpy tests had been performed before plates in all three states were tested for resistance to armour piercing 7.62×39 mm API BZ projectiles, on the proofing ground laboratory space.

Specimens for tensile tests were machined from the steel plates. Cylindrical specimens of dimensions shown in Fig. 2 standardized by EN ISO 6892-1:2009 standard [7] were used for testing. Hardness was measured using Vickers pyramid according to EN ISO 6507-4:2005 standard [8] and load of 98.1 N in three different locations from the upper side of the plate where later the armour piercing has been done. Three hardness measurements were taken at each location.

Charpy tests with ISO V-notch were done according to the ISO 14556 standard [9]. Tests were performed on 10×7.5×55 mm specimens Fig. 3 using an instrumented and new Vuhi-Charpy software [10].

Tests were performed at temperatures ‒40, ‒20, 0 and +20 °C. The VuhiCharpy software controls the Amsler RKP-300 Charpy pendulum and records the data of force and energy from the sensors during the impact.

Recording data enables to determine the force versus time diagram. The initial velocity during the impact (v0) is known from the mass and starting angle of the pendulum. Diagram velocity – time can be determined using Eq. 1.

1 t v(t ) = v0 − ∫ v(t )dt.

(1)

m t0 Diagram displacement versus time can be determined using Eq. 2.

1 t s (t ) = ∫ v(t )dt.

(2) m t0 Finally, diagram force versus displacement can be drawn. Area below of this diagram represents energy for fracture during the Charpy test. Energy can be calculated using Eq. 3.

s

E ( s ) = ∫ F ds. s0

(3)

Special acoustic sensor on the Charpy pendulum detects when crack starts to propagate. This sensor and SEP1315 standard [9] and [11] enable to split energy for initiation and energy for propagation from the total energy for fracture.

All three states were tested by armour piercing projectiles. 7.62×39 mm API BZ bullets were used (Fig. 4). Regarding the STANAG 4569 standard [12], the velocity of the projectile has to be 695±20 m/s.

The velocity was provided by the test rifle barrel with appropriate charge, and measured using two different methods.

Fig. 2. Specimen for tensile test

Fig. 3. Specimen for Charpy instrumented tests

Fig. 4. Bullets 7.62×39 mm API BZ for ballistic analyses

The first was using a radar (the average velocity of the projectile is assumed by the values of muzzle velocity and velocity of terminal flight phase of the bullet behind the tested plate), The second method of velocity measurements used an optical sensor placed in the terminal phase of the flight path (position of the sensor was 2 meters from test plate). The weapon used for the test was a M82 weapon gun, ranged on the distance of 30 m.

3 EXPERIMENTAL RESULTS 3.1 Tensile Test Results of the tensile test are shown in Figs. 5 to 8. Yield stress, tensile strength, elongation and contraction were measured. The yield strength results are presented in Fig. 5. Average values are marked for each plate signed as the A, B and C state as mentioned

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above. The highest values of tensile strengths were in plates of state C.

Contraction is highest in state C, which has the highest temperature of the tempering. The lowest contraction is in state A (only quenched).

3.2 Hardness Results Vickers hardness results are shown in Fig. 9. The highest hardness is in state A (only quenched).

Fig. 5. Yield stress of three different states

The tensile strength (Rm) results are shown in Fig. 6. The highest tensile strength is in state A and the lowest in state C. The highest Rp0.2/Rm ratio is in state A where the value is 0.662. The highest Rp0.2/Rm ratio is on state C where the value is only 0.806.

Fig. 9. Vickers hardness results of all three states

Tempering reduces the hardness [13]. Tempering at 220 °C reduces hardness from 569 to 533 HV10, but tempering at 280 °C reduces hardness to 525 HV10.

The highest scatter of hardness results is in state A. 3.3 Results of Charpy Test

Fig. 6. Tensile strength of three different states

The impact toughness of all three states is shown in Fig. 10. The highest impact toughness is in state B and the lowest is in state C. Tempering at 280 °C for 3 hours is not appropriate for the material because impact toughness is reduced. On the other hand, tempering at 220 °C for 3 hours improves impact toughness compared to quenched state.

Fig. 7. Elongation of three different states

Fig. 10. Impact toughness of three states

Fig. 8. Contraction of three different states

Elongation of all three states is approximately the same, around 12%. Results are shown in Fig. 7.

418

Fig. 11 is an example of the results of State C at +40 °C. For better armour protection it is important that the material has a higher energy needed for crack initiation, but the energy needed for the start of propagation is also consequential because it gives the material a chance to deform during the impact of the bullet. Figs. 12 to 14 show the total energy needed for

Bernetič, J. – Vuherer, T. – Marčetič, M. – Vuruna, M.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 416-421

breakage of the Charpy specimen, energy for crack initiation and crack propagation of all three states.

Fig. 14. Energy for propagation of three states

3.4 Microstructure Analyzes a)

b) Fig. 11. Instrumented Charpy test results;a) force to time, and b) energy to time; State C at +40 °C

Fig. 12. Total energy of three states

Fig. 15. Microstructures of all three states; a) State A, b) State B and c) State C Fig. 13. Energy for initiation of three states

Microstructures of all three steel states are imagined

by Olympus DP 71 CCD camera in the Olypmpus BX 51 M light microscope at magnification of 500×

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at resolution of 1360×1024 and shown in Fig. 11.

Samples were etched in 3% nital (3% HNO3 to 97% ethyl alcohol).

Fig. 15a shows lath martensite microstructure of the State A which was quenched, while Figs 15b and c are showing the States B and C which were tempered. Lath martensite microstructure and low tempered martensite can be observed in these samples. Low temperature tempering of the martensite microstructure is not used to transform martensite into other microstructure but just for the purpose of residual stress relaxation in the material [13] and [14].

The reduction of the mechanical properties (hardness, impact toughness, tensile strength) of the States B and C can be directly linked to the appearance of the ε carbide (Fe2.4C) as the consequence of the tempering. Additional research regarding the formation and effect of ε carbide (Fe2.4C) on mechanical properties will be done in near future using TEM microscopy.

front and back side. A smooth bulge can be observed from the rear of the plate.

3.5 Ballistic Resistance Results The angle of the test plates was aproximity 90° to the projectile aproaching direction. Fig. 16 shows a steel plate before and after the ballistic test. Five shots were fired into each plate. All measured bullet velocities were within the limits of the STANAG 4569 standard [12], which is presented in Table 2, for the values measured by radar and optical sensors. The results of the ballistic resistance test are also shown in Table 3.

Details of the frontal impact damage of shots 1 and 2 on the State A plate are presented in Fig. 17. No damage can be observed from the back side. Fig. 18 shows the impact damage on the same plate from the

Fig. 16. Test plate before and after the ballistic test

Fig. 17. Details of first and second shots hit damage on State A plate

Table 3. Results of the ballistic resistance of the steel plates State

State A

State B

State C

420

No. 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

V0 [m/s] 735.6 737.1 737.0 731.7 741.9 736.4 739.5 737.6 735.2 736.0 735.1 737.2 738.6 735.1 740.5

V28 [m/s] 705.0 707.5 707.2 701.8 710.6 705.8 709.9 707 705.6 706.4 705.7 708 709.6 705.7 711.9

Angle [°] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Distance [m] 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30

Bernetič, J. – Vuherer, T. – Marčetič, M. – Vuruna, M.

Description of the damage Deep impression in front, no damage at back Deep impression in front, no damage at back Smooth bulge at back Deep impression in front, no damage at back Deep impression in front, no damage at back Bulge at back without crack Bulge and crack at back, no light penetrating Bulge and crack at back, no light penetrating Bulge and crack at back, no light penetrating Bulge at back without crack Crack sufficient to see light trough Crack sufficient to see light trough Complete penetration Bulge and crack at back, no light penetrating Complete penetration

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 416-421

7 REFERENCES

Fig. 18. Details of shot 3 impact damage on state A plate from the front and back side

5 CONCLUSION Ballistic properties are a complex function of yield strength, tensile strength, hardness, ductility, charpy impact energy. An optimum combination of each property is essential for suitable ballistic performance and none of the properites alone are self sufficient to appropriately indicate the ballistic behaviour.

Appropriate ballistic performance as a result of good mechanical properties can be achieved by a suitable heat treatment.

Steel in a quenched condition (State A) has the lowest yield stress and highest tensile strength, so Rp0.2/Rm ratio is the lowest compared to steels which were quenched and low temperature tempered at 200 °C (State B) and 280 °C (State C). Lower values of the Rp0.2/Rm ratio indicate enhanced resistance to localised yielding which provides higher ballistic performance.

The highest hardness is in the quenched condition and the lowest in steel state C (quenched and tempered at 280 °C).

The impact toughness of the armour steel is the highest in steel state B but followed closely by the impact toughness of the just quenched condition in state A. The results of the best ballistic test obtained until today have shown that the highest ballistic resistance of the steel plates was in state A, which has the lowest Rp0.2/Rm ratio, the highest hardness, and nearly the highest impact toughness.

Lowered ballistic properties of States B and C can be linked to lowered properties between hardness, Rp0.2/Rm ratio and impact thougness and different ration between those properties.

6 ACKNOWLEDGMENT The presented paper has been made within project No 47029 financed by the Ministry of Science and Technology development Republic of Serbia.

[1] Baloh, S., Grabulov, V., Sidjanin, L., Pantić, M., Radisavljevic, I. (2010). Geometry, mechanical properties and mounting of perforated plates for ballistic application. Materials and Design, vol. 31, p.

2916-2924, DOI:10.1016/j.matdes.2009.12.031.

[2] Showalter, D., Gooch, W., Burkings, S., Montgomery, J.R.S. (2000). Development and balistic testing of new class of high hardness armor steel. The AMMTIAC Quaterly, vol. 4, no. 4, p. 3-6 [3] Rust, M. (2010). Passive protection Conepts. IBD Deisenroth Engineering, p. 33-37.

[4] Atapek, H.S.S.K. (2011). Ballistic impact behaviour of tempered ballistic steel against 7.62 mm armour piercing projectile. Defence Science Journal, vol. 61, p. 81-87.

[5] Nahme, H., Lach, E. (1997). Dynamic behaviour of high strength armor steels. Journal de Physique, vol. 7., no. C3, p. 373-378.

[6] Shah Khan, M.Z., Alkemade, S.J., Weston G.M. (1998).

Fracture Studies on High Hardness BISALLOY 500 Steel. Melbourne, DSTO-RR-0130.

[7] EN ISO 6892-1:2009 (2009). Metallic materials - Tensile testing - Part 1: Method of test at room temperature.

International Organization for Standardization, Geneva.

[8] EN ISO 6507-4:2005 (2005). Metallic materials Vickers hardness test - Part 4: Tables and hardness values), International Organization for Standardization, Geneva.

[9] ISO 14556:2000(E) (2000). Steel Charpy V-notch pendulum impact test – instrumented test method, ), International Organization for Standardization, Geneva.

[10] Vuherer, T. (2008). Analyze of microdefects on strenght at fatigue on coarse grain HEZ . University of Maribor, Faculty for Mechanical Engineering. Fakulteta za strojništvo, Maribor. (in Slovene) [11] STAHL – EISEN – Prüfblätter (SEP) des Vereins Deutscher Eisenhüttenleute, Kerbschlagbiegeversuch mit Ermittlung von Kraft und Weg (1987).

Empfehlungen zur Durchführung und Auswertung, SEP 1315, Verlag Stahleisen mbH, Düsseldorf.

[12] Nato standard - STANAG 4569 (2004). Protection levels for Occupants af Logistic and Light Armoured Vehicles, NATO, AEP-55.

[13] Smoljan, B., Iljkić, D. (2010). Predictions of mechanical properties of quenched and tempered steel. Strojniški vestnik - Journal of Mechanical Engineering, vol. 56, no. 2, p. 115-120.

[14] Liščić, B., Singer, C. (2010). Prediction of quenchhardness within the whole volume of axially-symmetric workpieces of any shape. Strojniški vestnik - Journal of Mechanical Engineering, vol. 56, no. 2, p. 104-114.

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Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 422-428 DOI:10.5545/sv-jme.2011.281

Paper received: 2011-12-20, paper accepted: 2012-04-24 © 2012 Journal of Mechanical Engineering. All rights reserved.

Experimental Investigation of High-Strength Structural Steel Welds

Ismar, H. – Burzic, Z. – Kapor, N.J. – Kokelj, T. Hajro Ismar1,*– Zijah Burzic2 – Nenad J.Kapor3 – Tugomir Kokelj4 1 University of Sarajevo, Faculty of Mechanical Engineering, Bosnia and Herzegovina 2 Military Technical Institute, Serbia 3 University of Belgrade, Faculty of Mechanical Engineering, Serbia 4 University of Defence, Military Academy, Serbia Material toughness becomes more significant material mechanical property, as well as design variable with recent advances of fracture mechanics understanding. Also, toughness is a particularly important parameter for novel structural materials such as high-strength steels.

Furthermore, due to the fact that high-strength steels are mainly used in various welded structures, evaluation of welded joint mismatched properties, including toughness, become particularly important. Therefore, the following paper presents investigation results of impact and quasi-static toughness distribution and mismatch on high-strength steels welds. Welded joint’s characteristic heterogeneous zones are obtained by mean of real welding and welding simulation. Finally, relation terms between various mechanical properties, including toughness, for further simplified engineering prediction are provided.

Keywords: toughness, fracture mechanics, high-strength steel, welds, mismatch.

0 INTRODUCTION Benefits of high-strength steels, HSS, are well known. However, to meet the necessary design and exploitation requirements for various steel structures, a number of factors must be considered wheb selecting HSS. These factors should include at least a reduced deformability, weldability and demanding toughness. Moreover, due to the unfavourable yield stress to tensile strength ratio, Y/T, and reduced ductility, those steels are mostly not allowed for use for some demanding steel structures due to the limitations set in design codes [1] to [4]. Development of novel structural integrity assessment procedures based on fracture mechanics, such as the international FITNET procedure [5], a more reliable and confident assessment is possible for various types of structures.

Here, the important property of materials, particularly of welded joints, the presence of material flaws, such as cracks, as well as material toughness and components stress state are required to assess particular component for a level of integrity. Moreover, there is a trend in national specifications, and in some international design codes for a particular type of structures, to apply fracture mechanics methods already in a design phase [6] and [7]. Furthermore, there is a trend that conventional qualification of welding procedures may require additional testing of fracture mechanics parameters on test coupons [5] to [7]. Never the less, a general toughness of high-strength structural steel present particular issue. However, toughness should be considered from the point of predicted or design loads. Therefore, according to fracture mechanics 422

principles, at least the following toughness parameters should be considered [5] and [8]: • Quasi-static toughness, represented by elastoplastic fracture mechanics, EPFM, resistance curves, e.g. J-Δa or CTOD-Δa; where J is J-integral in [kJ/m2], CTOD is crack tip opening displacement in [mm] and Δa is crack growth in [mm]; and characteristic initiation or materials critical values, e.g. JIc [kJ/m2], CTODIc [mm]; as well as linear-elastic fracture mechanic parameter, LEFM, fracture toughness, KIc [MPa·m0.5].

• Impact toughness, represented by resistance curves, KV-T or DL-T; where KV is total impact absorbed energy in [J], DL is percentage of shear fracture in [%], and T is testing temperature in [°C]; and therefore characteristic transition temperatures (depending on applied criteria), TT in [°C]. In addition, KV, may be evaluated for its parts, the so called crack initiation energy, KVi [J] and crack propagation energy, KVp [J].

Determination of KVi and KVp are also based on one kind of resistance curve, e.g. F-t, where F is impact force in [N] and t is time in [s] [4].

Furthermore, from the point of fracture mechanics and structural assessment procedures [5] to [10], a higher confidence and less conservatism may be achieved if material resistance properties, as well as applied stress condition are better known.

Here, another problem arises: Can sophisticated experimental evaluation of various fracture mechanics parameters, as well as stress state be performed?

Therefore, from the point of the fracture mechanics parameters evaluation, novel assessment procedures

*Corr. Author’s Address: University of Sarajevo, Faculty of Mechanical Engineering, Vilsonovo šetalište 9, Sarajevo, Bosnia and Herzegovina, hajro@mef.unsa.ba

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recognize approximation or relationship terms to evaluate rather “complicated” parameters, on basis of “simplified” ones. Even this paper does not deal with evaluation of stress state; various analytical and numerical approaches for evaluation of stress state are known.

It is not an intention of this paper to underestimate other general material toughness parameters, such as those related to dynamic-cyclic loads, e.g. material fatigue resistance, and corresponding fatigue resistance curves and appropriate critical values represented in known da/dN ‒ ΔK format, where da/dN is fatigue crack growth rate, e.g. da in [mm] and dN in [cycles] are crack growth and number of cycles, respectively, and ΔK [MPa·m0.5] is stress intensity factor.

Furthermore, because HSS are mainly used for the manufacturing of welded structures, welded joints resistance properties become particularly important.

Here, well known microstructural heterogeneity and mismatch of mechanical properties of a complete joint must be carefully considered and evaluated.

In addition, because welded joint presents typical structural joints with generated micro and macro faults (considered as cracks), the need for the application of fracture mechanics arises.

Therefore, this paper shows approach and experience on selected toughness properties investigation of HSS welds.

as the base materials (represented with carbon equivalent, CET, as shown in Table 1).

Table 1. Welding conditions steel thickness S690QL 30 mm S890QL 20 mm

preheat 200 °C 150 °C

Q

t8/5

1.4 to 1.8 kJ/m 6 to 8 s

CETBM 0.306 0.350

In Addition to specimens with an initial crack in the base, BM, and weld metal, WM, for evaluation of quasi-static toughness, an additional set of specimens for the evaluation of impact toughness is prepared with an initial notch in the base and weld metal, as well as in a heat affected zone, HAZ. The selection of welding parameters was made on the basis of good engineering experiences and a general recommendation given in EN 1011-2 [1] , [4] and [13], as well as on the basis of steel manufacturer recommendation, based on the optimum cooling time concept, e.g. t8/5, in range of 5 to 15 s. Typical specimen sampling plan is shown in Fig. 1.

1 EXPERIMENTAL PROCEDURE Similary to the tests in [11] and [12], which have evaluated the hardness of quenched and tempered (QT) steels for particular machine elements, related to cooling time t8/5 [13], as well as research work of structural steels in [1], this research has also considered and investigated two HSS QT steels: S690QL and S890QL according to EN 10025-6 (Q for quenched and tempered delivery condition; L for the required impact toughness of 27 J at -40 °C). On each steel, pairs of test coupons are butt welded, in PA (flat) position, using gas metal arc welding, GMAW, process and 82% Ar + 18% CO2 shielding gas.

Generally, described welding conditions are shown in Table 1. Filler materials (FM), delivered in accordance to EN 12534 [14], were G 69 5 M Mn3Ni1CrMo for S690QL, and G 89 6 M Mn4Ni2CrMo for S890QL, of 1.2 mm diameter, are selected on the basis of recommendation of a respective manufacturer. In fact, the FM was of a similar class (chemical composition and weld metal mechanical properties [2] and [14])

Fig. 1. Example of specimen sampling plan for the pairs of welded test coupons on steel S890QL

Due to the fact that a well known weakest weld zone within coarse-grain heat affected zone, CGHAZ, cannot be evaluated from real welds; additional specimens for welding simulation, and further impact toughness testing were prepared. Welding simulation was performed on thermo-mechanical simulator SmithWeld, in a condition similar than for real welding, e.g. for CG-HAZ with Tmax = 1300 °C, and t8/5 in range of 6 to 7 s (as shown for real welding on Table 1). In fact, the welding simulation correspond to the determined input thermo-cycle (Tmax, t8/5) [4].

Fig. 2 shows the applied thermo cycle for the welding simulation, as well as representative specimen during simulation.

Necessary initial testing consisting of chemical composition testing, hardness distribution testing and

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tensile testing were also performed. In addition, even if is not a subject of this paper, the microstructural evaluation of complete weld joints was performed.

Briefly, base metal consists of tempered martensitic microstructure; weld metal consists of dendrite low carbon martensitic microstructure, while HAZ consist of a mixture of martensitic–ferite–bainite microstructure. Appropriate weld joint hardness distribution is shown in Fig. 3. Therefore hardness mismatch, MM, or exactly the undermatching, UM, between weld and base metal, WM/BM, was in the range of MMHV = UMHV = 0.97 to 0.99. for both steel’s welded joints.

Welded joints macro sections as well as corresponding hardness distribution, tested in accordance to EN 1043-1 [15] are shown in Fig. 3.

a)

b) a)

Fig. 3. Welded joints macro section and hardness distribution; a) welded joint on S690QL, b) welded joint on S890QL

b) Fig. 2. a) Applied (measured) thermo cycles and b) typical specimen during welding simulation

In addition, results of tensile testing Fig. 4. show the following mismatch of strength and ductility, between weld and base metal, for both steel’s weld joints: • for yield stress, MM Rp02 = 0.89 to 0.96 , for tensile strength, MM Rm = 0.93 to 0.95, for cross-section contraction, MMz = 0.85 to 0.92.

Moreover, the general range of yield stress to tensile strength ratio, for both steel, for BM and WM, was found to be in the range of Y/T = 0.89 to 0.96.

• •

424

The resistance stress-strain curves, R-A Fig. 4, designated as PW present the results for specimen sampled perpendicular to the line of the welded joint.

Testing of such specimen is common for the welding procedure qualification.

2 RESULTS OF TOUGHNESS TESTING Typical resistance curves, F-t, of impact toughness testing using instrumented Charpy pendulum are shown in Fig. 5. The corresponding results of impact toughness testing on various testing temperatures are shown in Fig. 6.

The impact toughness testing were done in acc. to EN 10045-1 [16], while EPFM parameter testing was done in acc. to ASTM E1820 [9] and BS 7448-2 [10].

Each impact toughness specimen testing has provided

Ismar, H. – Burzic, Z. – Kapor, N.J. – Kokelj, T.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 422-428

a) b) Fig. 6. Total impact energy vs. testing temperature for specimens with initial notch in BM,HAZ and WM; a) welded joint on S690QL, b) welded joint on S890QL

a)

a)

b) Fig. 4. Typical results of tensile testing (resistance curves) of real welded joint specimens; a) welded joint on S690QL, b) welded joint on S890QL b)

a) c)

b)

c) Fig. 5. Typical results of impact toughness at room temperature with initial notch in a) BM, b) HAZ and c) WM

S690QL S890QL Fig. 7. Typical EPFM resistance curves for BM: a) F-COD, b) CTOD-Δa, c) J-Δa

appropriate results for KV, KVi, KVp and DL. The impact toughness dependence on testing temperature, from -100 to +20 °C (Fig. 6) shows that BM has the highest, while CG-HAZ has the weakest impact toughness. Without neglecting the lowest impact toughness found in CG-HAZ, the specimens from real welds, e.g. BM, WM and HAZ, have sufficient toughness as guarantied for BM in acc. to the standard for delivery condition, e.g. EN 10025-6, or KV > 27 J at -40 °C [2]. Also, KVi = 10 to 45 J presents a minor part of the total absorbed energy, KV, and a slight

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decrease with a temperature decrease, while KVp values follows the general trend of KV. Typical results of EPFM parameters testing, and the corresponding resistance curves, are shown in Figs. 7 and 8.

a)

is possible for corresponding results of hardness and tensile testing. These approximation terms may be particularly helpful for a further assessment of costly fracture mechanics parameters testing. The terms definition is based on similar approaches founded in novel integrity assessment procedures, such as FITNET, as well in respective scientific research works [8] and [9].

The obtained Eqs. (1) to (3), also presented in Fig. 9. were used for the calculation (prediction) of critical fracture mechanics parameters for HAZ and CG-HAZ, where the corresponding impact toughness, KV, was experimentally determined.

b) a)

c)

S690QL S890QL Fig. 8. Typical EPFM resistance curves for WM; a) F-COD, b) CTOD-Δa, c) J-Δa

Summarized range of critical materials EPFM and LEFM parameters testing are shown in Table 2.

Table 2. Critical material’s EPFM and LEFM parameters Specimen S690QL-BM S690QL-WM S890QL-BM S890QL-WM

JIc [kJ/m2] 201 to 238 117 to 133 173 to 188 111 to 126

CTODIc [mm] 0.25 to 0.27 0.12 to 0.13 0.14 to 0.15 0.10 to 0.11

KJIc [MPa·m0.5] 202 to 227 164 to 175 200 to 204 160 to 170

3 RELATIONSHIP TERMS If we consider experimentally obtained results of general toughness characteristics testing, both impact toughness, KV, and quasi-static toughness (critical fracture mechanics parameters), JIc, CTODIc, KJIc, it is possible to provide approximation terms. The same 426

c)

b)

d)

Fig. 9. Relationship terms between investigated mechanical properties of HSS welds; a) Rp0.2 = f(HV), b) KJIc = f(KV), c) JIc = f(CTODIc, Rp0,2), d) KJIc = f(JIc, E)

Finally, both experimentally obtained and by calculation approximated fracture resistance parameters are used to found the distribution of fracture resistance along welded joints, for both steels respectively, which is presented in Tables 3 to 6.

The following are obtained relationship terms Fig. 9, where E [GPa] stand for Young’s modulus:

K Ic = 18.94 ⋅ KV 0.461 , (1)

J Ic = 1.202 ⋅ (CTODIc ⋅ RP0.2 ), (2)

K Ic = 1.031 ⋅ J Ic ⋅ E . (3)

Ismar, H. – Burzic, Z. – Kapor, N.J. – Kokelj, T.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, 422-428

4 CONCLUSION The summarized preview of average toughness distribution, and corresponding undermatching, UM, for investigated welded joints are shown in Tables 3 to 6.

Table 3. Distribution of average impact toughness, KV [J], at room temperature (20 °C) Welded joint on S690QL UMtoBM S890QL UMtoBM

BM 194 160 -

HAZ 186 0.96 141 0.88

CG-HAZ 89 0.46 56 0.35

WM 127 0.65 104 0.65

Table 4. Distribution of average critical EPFM parameter, JIc [kJ/m2], at room temperature (20 °C) Welded joint on S690QL UMtoBM S890QL UMtoBM

BM 222 176 -

HAZ 201 0.91 148 0.85

CG-HAZ 90 0.41 54 0.31

WM 122 0.55 119 0.68

Table 5. Distribution of average critical EPFM parameter, CTODIc [mm], at room temperature (20 °C) Welded joint on

BM

HAZ

CG-HAZ

S890QL

0.26 0.22

0.26 1.00 0.19

UMtoBM

-

0.86

0.12 0.46 0.07 0.32

S690QL UMtoBM

WM 0.13 0.50 0.12 0.55

Table 6. Distribution of average critical LEFM parameter, KIc [MPa·m0.5], at room temperature (20 °C) Welded joint on

BM

HAZ

CG-HAZ

S690QL

227 202 -

205 0.90 177 0.88

137 0.60 107 0.53

UMtoBM S890QL UMtoBM

WM 168 0.74 166 0.82

Eqs. (1) to (3) presented in Fig. 9 for the approximation of fracture mechanics parameters, KJIc, JIc, CTODIc, based on the known impact toughness, KV, are valid only for welded joints executed with GMAW process, on high strength structural steels S690QL and S890QL respectively, in the thickness range of 20 to 30 mm. However, future research may include effects of specimens thickness and testing temperatures to adjust more precisely provided approximation terms. Also, a similar approach may be applied to other type of materials and their welded joints.

From the point of applied welding technology, it should be noted that welded joints on the subject HSS, e.g. S690QL and S890QL, are obtained by the use of preheating, but without post-weld heat-treatment, PWHT. This was possible in one way, by producing the slightly strength undermatching joints (UM = 0.89 to 0.96). Also, this strength undermatching is followed with generally acceptable toughness undermatching (Tables 3 to 6) which should be particularly included in any design or structural assessment, for such kind of materials and joints.

Therefore, evaluated complete welded joints resistance (particularly represented in strength and toughness) should provide more than a satisfactory confidence, with minimum conservatism.

The complete toughness undermatching, UM, of welded joint characteristic zone’s properties (in comparison to base metal, BM) are found to be on the following lowest limits (from Tables 3 to 6): • 0.85, for real HAZ, • 0.31, for simulated CG-HAZ, • 0.50, for real WM. Finally, the presented investigation and characterization approach, as well as the obtained results, could be helpful for a future setting of new acceptance criteria based on fracture mechanics parameters, or general toughness.

5 ACKNOWLEDGMENT The presented paper has been made within project No 47029 financed by the Ministry of Science and Technology Development Republic of Serbia.

6 REFERENCES [1] Kaiser, H.J., Kern, A., Niesen, T., Schriever, U. (2001).

Modern high-strength steels with minimum yield strength up to 690 MPa and high component safety, Proceedings of the 11th International Offshore and Polar Engineering Conference, Stavanger.

[2] EN 10025-6 (2004). Hot rolled products of structural steels, Part 6: Technical delivery conditions for flat products of high yield strength structural steels in the quenched and tempered condition. European Committee for Standardization, Brussels.

[3] High-strength heavy plates (2008). Weight savings combined with excellent weldability. VoestAlpine Grobblech, Linz.

[4] Hajro, I., Pasic, O., Burzic, Z. (2010). Characterization of welded joints on high-strength structural steels S690QL and S890QL. 2nd South-East European IIW International Congress, Sofia.

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[5] Gutierrez-Solana, C., Alvarez, L. (2001). FITNET – Basic Training Package. University of Cantabria, Cantabria.

[6] M-120 (2000). Material data sheets for structural steel, Norsok standard. Norwegian Technology Center, Oslo.

[7] M-101 (2000). Structural steel fabrication, Norsok standard. Norwegian Technology Center, Oslo.

[8] Fujita, H., Tanaka, M., Kamiya, O. (1982). Temperature dependence of JIc fracture toughness values in the structural steels and evaluation of the testing method.

Transactions of the Iron and Steel Institute of Japan, vol. 22, no. 2.

[9] ASTM E1820 (2001). Standard test method for measurement of fracture toughness. Annual Book of ASTM Standards, vol. 03.01.

[10] BS 7448-2 (1997). Fracture mechanics toughness tests - Part 2. Method for determination of KIc, critical CTOD and critical J values of welds in metallic materials. British Standard Institute, London.

[11] Smoljan, B., Iljkić, D. (2010). Predictions of mechanical properties of quenched and tempered steel.

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Strojniški vestnik - Journal of Mechanical Engineering, vol. 56, no. 2, p. 115-120.

[12] Liščić, B., Singer S., Smoljan, B. (2010). Prediction of quench-hardness within the whole volume of axiallysymmetric workpieces of any shape. Strojniški vestnik - Journal of Mechanical Engineering, vol. 56, no. 2, p.

104-114.

[13] EN 1011-2:2004. Welding - Recommendations for welding of metallic materials, Part 2, Arc welding of ferritic steels. European Committee for Standardization, Brussels.

[14] EN 12534:1999. Welding consumables - Wire electrodes, wires, rods and deposits for gas shielded metal arc welding of high strength steels – Classification.

European Committee for Standardization, Brussels.

[15] EN 1043-1:1996. Destructive tests on welds in metallic materials. Hardness testing. Hardness test on arc welded joints. European Committee for Standardization, Brussels.

[16] EN 10045-1:1990. Charpy impact test on metallic materials. Test method (V- and U-notches). European Committee for Standardization, Brussels.

Ismar, H. – Burzic, Z. – Kapor, N.J. – Kokelj, T.

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6 Vsebina

Vsebina Strojniški vestnik - Journal of Mechanical Engineering letnik 58, (2012), številka 6 Ljubljana, junij 2012 ISSN 0039-2480 Izhaja mesečno

Gostujoči uvodnik

SI 73

Razširjeni povzetki člankov Zoran Jakšić, Momčilo Milinović, Danijela Randjelović: Nanotehnološka izboljšava infrardečih detektorjev s plazmonsko resonanco v nanodelcih transparentnega prevodnega oksida Branko Livada, Radomir Janković, Nebojša Nikolić: Elektronika oklepnih bojnih vozil: kriteriji snovanja prikazovalnikov Milenko Andrić, Boban Bondžulić, Bojan Zrnić, Aleksandar Kari, Goran Dikić: Analiza eksperimentalnih akustičnih podatkov odbojev na premikajočih se tarčah, opazovanih z Dopplerjevim radarjem Momčilo Milinović, Damir Jerković, Olivera Jeremić, Mitar Kovač: Preizkušanje stabilnosti vrtenja med letom topovskega izstrelka malega kalibra z eksperimentom in simulacijo Slobodan Jaramaz, Dejan Micković, Predrag Elek, Dragana Jaramaz, Dušan Micković: Model za snovanje bojnih glav z oblikovanim polnilom Martin Macko, Slobodan Ilić, Mirko Jezdimirović: Vpliv dimenzij delov in velikosti toleranc na sprožilno karakteristiko Jure Bernetič, Tomaž Vuherer, Matjaž Marčetič, Mladen Vuruna: Preliminarne preiskave nove generacije oklepne pločevine za lahka oklepna vozila Hajro Ismar, Zijah Burzic, Nenad J. Kapor, Tugomir Kokelj: Eksperimentalna raziskava zvarnih spojev visokotrdnostnih konstrukcijskih jekel Osebne vesti Doktorske disertacije, znanstvena magistrska dela, specialistična dela, diplomske naloge

SI 75 SI 76 SI 77 SI 78 SI 79 SI 80 SI 81 SI 82 SI 83

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6 Gostujoči uvodnik

Gostujoči uvodnik Tematska številka: K interdisciplinarnim raziskavam v naprednih tehnologijah

Celovito izboljševanje zmogljivosti izdelkov je običajno predmet razvoja posebnih ozko usmerjenih disciplin na različnih področjih sodobnih tehnologij, izkazuje pa se skozi nove dosežke in rezultate aplikativne znanosti. Ta številka SV-JME lahko pomaga pri identifikaciji smeri delovanja na različnih integrativnih področjih strojništva v povezavi s posebnimi raziskovalnimi temami, s končnim ciljem iskanja ravnovesja med zahtevami raziskav ustreznih aplikativnih znanosti in potrebami po novih tehnoloških dosežkih. V številki je osem člankov, ki so razdeljeni v tri tematske skupine in predstavljajo uporabne raziskave na področju mehatronike, posebnih inženirskih tem in tehnologij jekla.

Tematski sklop o mehatroniki je zastopan s tremi članki. Prvi z naslovom Nanotehnološka izboljšava infrardečih detektorjev s plazmonsko resonanco v nanodelcih transparentnega prevodnega oksida obravnava problematiko informacijskih in komunikacijskih senzorskih tehnologij. Delo predstavlja prispevek k sodobnim raziskavam novih materialov v mehatroniki in se ukvarja s strategijami za izbiro nanotehnoloških parametrov pri razvoju mikrosenzorskih elementov. Nove zmogljivosti so uporabne pri razvoju manjših vodenih izstrelkov, izsledki pa bodo koristni tudi na drugih aplikativnih področjih, ki vključujejo svetlobne senzorje. Predmet drugega članka z naslovom Elektronika oklepnih bojnih vozil: kriteriji snovanja prikazovalnikov so posebne tehnologije upravljanja, integrirane v vozila, ki delujejo v izjemno zahtevnih pogojih. Delo podaja pregled ter odpira vprašanja za diskusijo o kakovosti opreme vozil, ki vključuje najrazličnejše tehnologije. Naslednji prispevek iz področja mehatronike pod naslovom Analiza eksperimentalnih akustičnih podatkov odbojev na premikajočih se tarčah, opazovanih z Dopplerjevim radarjem je posvečen metodologiji zaznavanja in prepoznavanja oddaljenih ciljev človeškega izvora. Delo predstavlja rezultate raziskav v obliki zbirke podatkov, ki so prosto dostopni na spletni strani za uporabnike in raziskovalce po vsem svetu.

Drugi tematski sklop predstavlja rezultate integrativnih raziskav na področjih uporabne mehanike, konkretno aplikacije posebnih inženirskih tem. Delo Preizkušanje stabilnosti vrtenja med letom topovskega izstrelka malega kalibra z eksperimentom in simulacijo se ukvarja z integracijo dinamike rotacijskega gibanja med letom in aerodinamike. Izviren prispevek avtorjev je povezava matematičnih simulacij in eksperimentalnih preizkusov za vrteče se premične objekte. Prispevek z naslovom Model za snovanje bojnih glav z oblikovanim polnilom združuje posebno lomno mehaniko in mehaniko plinskih eksplozij z eksperimentalno preverjeno programsko opremo, ki so jo razvili avtorji. Tretje delo Vpliv dimenzij delov in velikosti toleranc na sprožilno karakteristiko raziskuje odvisnosti med natančnim projektiranjem v mehaniki in posledicami pri dinamičnih učinkih. Delo je podprto s simulacijami, opravljenimi s programsko opremo avtorjev. Tema je pomembna za posebno in natančno inženirstvo.

Tretja skupina člankov predstavlja dosežke na področju raziskav tehnoloških vplivov na lastnosti jekla kot osnovnega konstrukcijskega materiala v strojništvu. Članka Preliminarne preiskave nove generacije oklepne pločevine za lahka oklepna vozila ter Eksperimentalna raziskava zvarnih spojev visokotrdnostnih konstrukcijskih jekel obravnavata vpliv proizvodnje in uporabljenih tehnologij na končne zahteve jeklenih materialov in njihove konstrukcijske značilnosti.

Namesto zaključka želim poudariti, da je ta številka SV-JME v kontekstu okrepljenih razvojnih raziskav lahko skromen dokaz dejstva, da so projektanti in raziskovalci prepoznali pomen boljšega povezovanja ter uporabe znanstvenih rezultatov in njihovih tehnoloških aplikacij na posebnih področjih inženirstva. To je pomembno tudi za splošno raven tehnološkega razvoja, ki mora biti predmet diskusij in cilj za prihodnost.

Gostujoči urednik, Prof. dr. Momčilo Milinović SI 73

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Prejeto: 2011-12-20, sprejeto: 2012-03-21 © 2012 Strojniški vestnik. Vse pravice pridržane.

Nanotehnološka izboljšava infrardečih detektorjev s plazmonsko resonanco v nanodelcih transparentnega prevodnega oksida Jakšić, Z. – Milinović, M. – Randjelović, D. Zoran Jakšić1,* – Momčilo Milinović2 – Danijela Randjelović1

1 Univerza

v Beogradu, Institut za kemijo, tehnologijo in metalurgijo, Srbija v Beogradu, Fakulteta za strojništvo, Srbija

2 Univerza

Izboljšava odzivnosti in specifične občutljivosti srednje- in dolgovalovnih polprevodniških infrardečih (IR) fotodetektorjev brez kriogenega hlajenja je cilj intenzivnih raziskav v skupnosti, ki se ukvarja z razvojem IRtehnologij. Polprevodniški IR-detektorji običajno zagotavljajo najvišjo hitrost odziva in so prva izbira za vojaške sisteme. Cilj članka je predstavitev možne nanotehnološke rešitve za visokoobčutljive in cenovno ugodne infrardeče polprevodniške detektorje, ki bodo uporabni za različne namene, vključno z najzahtevnejšimi vojaškimi aplikacijami.

Obravnavane so možnosti uporabe plazmonske nanotehnologije za izboljšano upravljanje s svetlobo v polprevodniških IR-fotodetektorjih. Povečanje kvantne učinkovitosti, odzivnosti in specifične občutljivosti je doseženo z uporabo transparentnih nanodelcev prevodnega oksida (TCO). Predmet študije so bile nehlajene fotoprevodne naprave iz živosrebrovega kadmijevega telurida (HgCdTe), izdelane s strjevanjem iz parne faze.

Enak postopek je uporaben tudi za kriogeno hlajene naprave, vključno s tistimi fotonapetostnega tipa.

Glavni mehanizem za izboljšavo je koncentracija svetlobe, dosežena z lokalizirano plazmonsko resonanco nanodelcev TCO in z izboljšanim sipanjem, želeno območje valovnih dolžin pa je doseženo z dodatnim rdečim premikom, ki izhaja iz prilagoditve lastnosti nanodelcev. Za izboljšanje vzorčnih detektorjev so bili obravnavani nanodelci cinkovega oksida, dopirani z aluminijem, ter delci kositrovega oksida, izdelani po nevodnem postopku.

Obravnavanih je bilo tudi več konfiguracij za izboljšavo fotodetektorjev z nanodelci iz transparentnega prevodnega oksida ter polnimi oksidnimi plasti. Cilj je bil optimizacija območja delovnih valovnih dolžin z rdečim premikom optičnih lastnosti nanodelcev. Plazemska frekvenca TCO je v primerjavi s kovinskimi nanodelci že sama po sebi rdeče premaknjena, z dopiranjem pa jo je mogoče še dodatno prilagoditi. Obravnavana je bila tudi strategija doseganja rdečega premika z vdelavo plazmonskih nanodelcev TCO v medij z vrednostjo lomnega količnika, ki presega njegovo vrednost pri nanodelcih. Druga metoda za prilagoditev položaja vrha prereza sipanja je bila z vplivanjem na gostoto nanodelcev, t. j. z vplivanjem na razdaljo med njimi. Obravnavani so tudi tehnološki postopki za implementacijo predlagane izboljšave pri obstoječih vrstah IR-detektorjev HgCdTe. Ugotovljeno je bilo, da predlagana strategija izboljšuje upravljanje s svetlobo in s tem tudi značilnosti detektorja. Analiza realnih nehlajenih fotoprevodnikov HgCdTe izkazuje izboljšanje specifične občutljivosti za faktor 2 do 2,5, ki je močno odvisno od dejanske debeline kadmijevega dela epitaksialne plasti z najmanjšo molsko maso. Prednost TCO je ta, da so absorbcijske izgube manjše kot pri standardnih plazmonskih kovinah kot so zlato, srebro itd. Uporaba TCO ponuja še dodatno svobodo pri snovanju fotodetektorjev, kar prispeva k enostavnosti in stroškovni učinkovitosti.

Prihodnje raziskave morajo biti usmerjene v uporabo nanodelcev TCO na obstoječih vrstah infrardečih fotodetektorjev, zlasti nehlajenih. Za optimizacijo naprav je treba preučiti različne materiale TCO in različne tehnološke parametre, vključno z ravnmi dopiranja.

Avtorjem niso znani prejšnji poskusi plazmonske izboljšave s transparentnimi prevodnimi oksidi pri srednjein dolgovalovnih infrardečih detektorjih. Izboljšano upravljanje s svetlobo je zelo pomembno pri tankoslojnih fotodetektorjih in predlagani pristop bi lahko postal uporabna alternativa za najrazličnejše aplikacije, celo najzahtevnejše kot so naprave za sledenje pri pametnih izstrelkih.

Ključne besede: nanotehnologija, plazmonika, samovodena glava, infrardeči detektorji, plazmonska izboljšava, transparentni kovinski oksidi, nanodelci, transparentni prevodni oksidi

*Naslov avtorja za dopisovanje: Univerza v Beogradu, Institut za kemijo, tehnologijo in metalurgijo, Njegoševa 12, 11000 Beograd, Srbija, jaksa@nanosys.ihtm.bg.ac.rs

SI 75

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 76

Prejeto: 2011-12-20, sprejeto: 2012-05-18 © 2012 Strojniški vestnik. Vse pravice pridržane.

Elektronika oklepnih bojnih vozil: kriteriji snovanja prikazovalnikov Livada, B. – Janković, R. – Nikolić, N. Branko Livada1 – Radomir Janković2 – Nebojša Nikolić3 1 Luxell Technologies Ltd., Kanada 2 Univerza Union, Fakulteta za računalništvo, Srbija 3 Institut za strateške raziskave, Srbija

Nedavne izboljšave na področju informacijskih tehnologij in oklepnih bojnih vozil (AFV) nakazujejo nove smeri na področju razvoja elektronskih naprav za upravljanje vozil in nov taktični pristop k uporabi AFV na bojišču.

Kljub temu, da so v aktivni uporabi že skoraj 100 let, so oklepna bojna vozila še vedno eno najpomembnejših sredstev vsakih sodobnih kopenskih sil. Pri sodobnem vojskovanju se je občutno spremenil način uporabe oboroženih sil, kar je privedlo do potrebe po raziskavah in uvedbi novih taktičnih postopkov, pri čemer je najbolj obetavno rojenje. Rojenje v vojaškem pomenu besede pomeni sistematično impulzno delovanje s strani razpršenih, v omrežje povezanih enot, za sočasen napad iz vseh smeri.

Za uporabo oklepnih bojnih vozil v rojih (srednjih tankov, bojnih transporterjev, izvidniških vozil itd.) je treba razviti ustrezen sistem C4ISR z računalniki, navigacijo in prikazovalniki za interakcijo s posadko. Elektronika vozil (vetronika) zato postaja ključni del tako pri novih oklepnih bojnih vozil kot pri nadgradnjah obstoječih vozil.

Prikazovalnik je ena ključnih komponent sistema C4ISR in kot integrirani del opreme omogoča posadki AFV dostop do vseh informacij, potrebnih za upravljanje z gibanjem in delovanjem njihovih oklepnih bojnih vozil. Omogoča jim sodelovanje v vseh skupnih dejanjih oklepnih bojnih vozil, ki uporabljajo taktiko rojenja: nadzorovano gibanje in delovanje v roju, ter aktivno sodelovanje v sistemu C4ISR v vlogi vira in prejemnika informacij. Članek obravnava osnovne funkcionalnosti in lastnosti prikazovalnikov za sodobna oklepna bojna vozila in predstavlja osnovo za ugotavljanje priložnosti za uporabo različnih tehnologij v zahtevnem okolju AFV. Za prikazovalnike oklepnih bojnih vozil so značilni aktivno območje, fizična velikost in druge značilnosti, kot so svetlost, ločljivost, vidni kot, barva, sivinska skala, funkcija nočnega vida in berljivost v sončni svetlobi.

Obravnavane so tudi nekatere posebne zahteve glede lastnosti prikazovalnikov oklepnih bojnih vozil v okolju uporabe AFV. Članek podaja tudi pregled ključnih tehnologij pri snovanju prikazovalnikov AFV in njihovo skladnost z osnovnimi zahtevami. Kot možni kandidati za uporabo v AFV so obravnavane naslednje tehnologije prikazovalnikov: sevalne tehnologije prikazovalnikov (katodna cev – CRT, poljska emisija – FED, svetleče diode – LED, elektroluminiscenčni prikazovalnik – ELD, plazemski – PDP, organske svetleče diode – OLED), kakor tudi nesevalne tehnologije (tekoči kristali – LCD in osnovne tehnologije AMLCD, ki določajo strukturo panela AMLCD: zasukana nematična – TN, super zasukana nematična – STN, vertikalna poravnava (večdomenska vertikalna poravnava) - VA (MVA), preklapljanje v ravnini (napredno preklapljanje z električnim poljem) - IPS (AFFS), mikro elektromehanski sistemi - MEMS in projekcijski prikazovalniki).

Ko obstaja potreba po dodatnih značilnostih prikazovalnika za posebne aplikacije (široko temperaturno območje in neugodni vplivi okolja, visoka zanesljivost in dolga življenjska doba, berljivost pri zelo svetlem okolju itd.), je treba poiskati robustno rešitev prikazovalnika. Odvisno od aplikacije je mogoče uporabiti različne ravni robustne izvedbe in ustrezne tehnične rešitve. Danes se najpogosteje uporabljajo komercialni paneli AMLCD, ki so ustrezno prilagojeni za konkretne aplikacije. Postopek prilagoditve za večjo robustnost običajno vključuje naslednje inženirske rešitve in spremembe: mehanska zasnova, električna/hardverska zasnova, zasnova programske opreme (vdelane), optična zasnova, ohišje, mehanski vmesnik in končno robusten prikazovalnik kot najpomembnejši del sistema.

V aplikacijah za oklepna bojna vozila prevladujejo komercialni ploski zasloni AMLCD v robustni izvedbi in vse kaže, da bodo svoje mesto v oklepnih bojnih vozilih ohranili tudi v prihajajočem desetletju.

Ključne besede: elektronika vozil, rojenje, zasloni za oklepna bojna vozila, robustni zasloni, tehnologija AMLCD, ploski zasloni

SI 76

*Naslov avtorje za dopisovanje: Luxell Technologies Ltd., Mississauga, Kanada, blivada@luxell.com

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 77

Prejeto: 2011-12-20, sprejeto: 2012-04-25 © 2012 Strojniški vestnik. Vse pravice pridržane.

Analiza eksperimentalnih akustičnih podatkov odbojev na premikajočih se tarčah, opazovanih z Dopplerjevim radarjem Andrić, M. – Bondžulić, B. – Zrnić, B. – Kari, A. – Dikić, G. Milenko Andrić1,* – Boban Bondžulić1 – Bojan Zrnić2 – Aleksandar Kari1 – Goran Dikić1 1 Univerza za obrambo, Vojaška akademija, Srbija 2 Ministrstvo za obrambo, Oddelek za obrambno industrijo, Srbija

Glavna naloga radarjev za opazovanje na kopnem, namenjenih varovanju in krožni zaščiti, je zaznavanje in klasifikacija premikajočih se kopenskih ciljev. Pri tipičnih radarskih sistemih je zaznavanje ciljev popolnoma avtomatizirano, pri klasifikaciji tarč pa se morajo vključiti tudi ljudje. Pri večini aplikacij radarjev za opazovanje na kopnem se klasifikacija premikajočih se ciljev izvaja s pomočjo njihovega zvočnega Dopplerjevega podpisa.

Dopplerjev pojav opisuje premik srednje frekvence sprejete valovne oblike zaradi relativnega gibanja cilja glede na radar. Radar iz Dopplerjeve frekvence premikajočih se tarč ustvari zvočni signal in razrede pomembnih kopenskih ciljev je mogoče razlikovati po njihovem zvočnem Dopplerjevem podpisu. Operater posluša zvočni kanal in prepoznava premikajoče se cilje po njihovem zvočnem Dopplerjevem podpisu. Takšen pristop pa je nezadovoljiv, saj ga omejujejo čutila človeškega operaterja.

Naš cilj je izdelava uravnotežene in izčrpne zbirke podatkov, ki omogoča ponovljive rezultate raziskav na področju klasifikacije premikajočih se ciljev na kopnem (prepoznavanje vzorcev).

V članku so obravnavani sprejeti podatki radarskih odbojev na premikajočih se ciljih na kopnem ter ustrezni signali v časovno-frekvenčnem prostoru z uporabo spektrograma in kepstra. Zbirka podatkov, imenovana RadEch, vsebuje radarske odboje različnih ciljev. Namen tega članka je identifikacija in validacija značilnosti različnih razredov ciljev, temu pa sledi izbira glavnih značilnosti za klasifikacijo. Podatki so bili zbrani v nadzorovanem preizkusnem okolju na lokaciji Vojaške akademije v Republiki Srbiji. Zbirka podatkov RadEch je prosto dostopna za prenos in upamo, da jo bodo raziskovalci lahko uporabili kot orodje za primerjavo in izboljšanje zmogljivosti klasifikacijskih algoritmov.

Za iskanje najosnovnejših informacij, ki jih je mogoče uporabiti za klasifikacijo, je bila uporabljena spektralna analiza: sredinska Dopplerjeva frekvenca, širina spektralnega pasu okrog sredinske Dopplerjeve frekvence in kadenčna frekvenca. Razvili in analizirali smo kepstralne koeficiente realnih zvočnih (akustičnih) radarskih signalov. Izkazalo se je, da dajeta drugi in tretji kepstralni koeficient obetavne informacije o sredinski Dopplerjevi frekvenci, peti in šesti kepstralni koeficient pa dajeta obetavne informacije o spektralni širini okrog sredinske frekvence. Na ta način smo pokazali odvisnost med kepstralnimi koeficienti ter sredinsko Dopplerjevo frekvenco in spektralno širino okrog nje.

S skrajšanjem trajanja sekvenc se približajo realni kepstralni koeficienti različnih razredov, kar je mogoče pojasniti s tem, da ni dovolj informacij za ustrezno ločitev razredov.

Za iskanje najosnovnejših informacij, ki jih je mogoče uporabiti za klasifikacijo, je bila v tem članku uporabljena analiza na osnovi kepstra. Ti podatki bodo v nadaljnjem delu uporabljeni za razvoj kepstralnih klasifikacijskih algoritmov kot osnove za programsko in strojno opremo za samodejno prepoznavanje. V prihodnjem delu bomo tudi razširili zbirko podatkov z novimi razredi ciljev (tanki, helikopterji, živali). Pripravili bomo tudi zbirko podatkov za zaznavanje ciljev in klasifikacijo.

Ključne besede: zbirka podatkov radarskih odbojev, Dopplerjev podpis, spektrogram, kepster, iskanje značilnosti, klasifikacija

*Naslov avtorja za dopisovanje: Univerza za obrambo, Vojaška akademija, Pavla Jurišica Šturma 33, Beograd, Srbija, asmilenko@beotel.net

SI 77

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 78

Prejeto: 2011-12-20, sprejeto: 2012-04-03 © 2012 Strojniški vestnik. Vse pravice pridržane.

Preizkušanje stabilnosti vrtenja med letom topovskega izstrelka malega kalibra z eksperimentom in simulacijo Milinović, M. – Jerković, D. – Jeremić, O. – Kovač, M. Momčilo Milinović1,* – Damir Jerković2 – Olivera Jeremić1 – Mitar Kovač2 1 Univerza v Beogradu, Fakulteta za strojništvo, Srbija 2 Univerza za obrambo, Vojaška akademija, Srbija

Glavni namen članka je obravnava korelacij med kriteriji stabilnosti leta, izpeljanih v obliki povezav med aerodinamičnimi koeficienti in odvodi, na modelu topovskega izstrelka malega kalibra s stabiliziranim vrtenjem.

Motivacija za raziskavo je modernizacija 40-milimetrskih protiletalskih topovskih izstrelkov za razširjeno uporabo topov v novih taktičnih situacijah. Razvoj sodobnega streliva je v zadnjih dvajsetih letih razširil področje uporabe tehnologij natančnega vodenja in krmiljenja tudi na taktično strelivo manjšega kalibra. Protiletalski izstrelki brez vodenja se uporabljajo predvsem za delovanje po zračnih tarčah, streljanje z balističnimi trajektorijami, pojavljajo pa se tudi razmisleki o njihovi uporabi na ciljih na tleh. Analiza je bila osredotočena na spremembe zasnove vodenja, ki je zaradi posebnih značilnosti nevodenega leta izstrelkov poseben izziv za strelivo protiletalskih topov z omejenimi možnostmi uporabe tehnologij vodenja.

Modeli za izračunavanje kriterijev stabilnosti so postavljeni na osnovi eksperimentalnih preizkusov aerodinamičnih podatkov v vetrovniku in polempiričnih podatkov, oboji podatki pa se uporabljajo za simulacijo stabilnosti trajektorije leta. Rezultati preizkusov v vetrovniku in izračunane vrednosti aerodinamičnih koeficientov, kot funkcij Machovega števila modela izstrelka, so vključeni kot kriteriji stabilnosti simulirane trajektorije leta.

Opravljena je primerjalna analiza eksperimentalnih in izračunanih aerodinamičnih koeficientov modela izstrelka, ki določajo kriterije stabilnosti leta. Izračunani odvodi aerodinamičnega Magnusovega momenta izstrelka in druge aerodinamične značilnosti so uporabljene kot faktorji kritične stabilnosti za podatke preizkusov v primerjavi z Machovim številom leta. Predstavljeni so vplivi odsotnosti in prisotnosti tega odvoda na modelni vrsti trajektorije leta za oceno faktorjev dušenja in stabilnosti naletnega kota. Prikazani so simulacijski preizkusi nadzvočne in podzvočne integralne hitrosti leta ter podatki za dušenje vrtenja. Ta metodologija, ki obsega polempirične matematične simulacije funkcije leta izstrelkov in eksperimentalne preizkuse njihovih aerodinamičnih lastnosti v pogojih stacionarnih preizkusov, je vključena v snovanje novega aerodinamičnega okvirja. Metoda uporablja brezdimenzijsko Machovo število za spremembo pogojev hitrosti leta v spremenljivih pogojih stacionarnih preizkusov, ki se izvajajo v vetrovniku. Popolna korelacija med obema primeroma je žal lahko samo približna, vendar je dovolj natančna za veljavne zaključke.

Sprememba izračunanih vrednosti aerodinamičnih koeficientov se ujema z eksperimentalnimi meritvami aerodinamičnih koeficientov, ne izpolnjuje pa pogojev stabilnosti brez merjenja odvodov. Preizkušen je primerjalni računski model za ocenjevanje koeficientov, ki omogoča iskanje morebitnih neznank, ki bi lahko bile signifikantne, vendar niso bile ugotovljene pri meritvah v vetrovniku v pogojih približno stacionarnega stanja.

Nadaljnje raziskave posodobitev streliva lahko vključujejo novo metodologijo za simulacijo stabilnosti bočnih sil v povezavi z metodo odvodov koeficientov, ki je predstavljena v tem članku, obravnavo približnih vrednosti Magnusovih momentov in drugih podobnih motenj, ki se odražajo v vrednostih odvodov koeficientov. Raziskava je obsegala tako simulacije kot preizkuse za iskanje najboljšega načina vodenja streliva na osnovi vedenja glavnih osi izstrelka in hitrostnega vektorja med letom.

Ključne besede: aerodinamični koeficienti, topovski izstrelek malega kalibra s stabiliziranim vrtenjem, faktor žiroskopske stabilnosti, faktor dinamične stabilnosti, koeficienti stabilnosti dušenja

SI 78

*Naslov avtorja za dopisovanje: Univerza v Beogradu, Fakulteta za strojništvo, Kraljice Marije 16, Beograd, Srbija, mmilinovic@mas.bg.ac.rs

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 79

Prejeto: 2011-12-20, sprejeto: 2012-03-21 © 2012 Strojniški vestnik. Vse pravice pridržane.

Model za snovanje bojnih glav z oblikovanim polnilom

Jaramaz, S. – Micković, D. – Elek, P. – Jaramaz, D. – Micković, D. Slobodan Jaramaz1 – Dejan Micković1,* – Predrag Elek1 – Dragana Jaramaz2 – Dušan Micković1 1 Univerza v Beogradu, Fakulteta za strojništvo, Serbia 2 Univerza UNION-Nikola Tesla, Fakulteta za gradbeništvo, Serbia Oblikovana polnila so izjemno učinkovita, kadar je za preboj ovir potrebna intenzivna in lokalizirana sila. Glavno področje uporabe je v vojaški industriji za visokoeksplozivne protitankovske izstrelke (HEAT), vključno z izstrelki ročnih raketnih metalcev, tromblonskimi minami, topovskimi izstrelki in različnimi vrstami bomb. Njihovi cilji so oklepi, bunkerji, betonske ali geološke utrdbe in vozila.

Oblikovano polnilo je bilo analizirano z analitičnim pristopom v preliminarni analizi in s parametričnimi študijami za ugotovitev približne zasnove, ki bi lahko izpolnila tehnične zahteve. V ta namen so bili razviti modeli za naslednje faze: ocenitev eksplozivnih lastnosti, lastnosti in profila detonacijskega vala, izračun hitrosti plašča, izračun hitrosti in kota kolapsa plašča, določitev dolžine curka oblikovanega polnila in ocenitev penetracije cilja.

Ti modeli so vključeni v računalniško kodo CUMUL. Eksplozivne lastnosti, kot so Chapman-Jouguetov tlak, detonacijska hitrost in Gurneyjeva konstanta, so izračunane s pomočjo empiričnih enačb. Za določitev profila detonacijskega vala je bil uporabljen model logaritmične spirale. Obravnavane so štiri različne oblike plašča: konična, parabolična, bikonična in Gaussova. Ko detonacijski val prispe do plašča, se plašč pospeši do začetne hitrosti. CUMUL uporablja štiri pristope za izračun začetne hitrosti: asimetrični sendvič, Gurneyjevo formulo za implozijo valja, Chanteretovo formulo in Hirschevo formulo. Privzeto je, da hitrost plašča po kolapsu sledi profilu takojšnjega, konstantnega ali eksponencialnega pospeševanja. Izračunani so začetna dolžina, masa, premer, čas prihoda in hitrost prihoda curka v trenutku nastanka curka. Čas razpršitve je najdaljši čas raztezanja curka, preden se ta razprši v delce. CUMUL upošteva dve formuli za ocenjevanje časa razpršitve za oblikovano polnilo. Po določitvi časa razpršitve se izračuna največji raztezek curka, s tem pa končna ali celotna dolžina curka.

Obravnavani so pojavi pri penetraciji in predstavljene so vodilne enačbe. Prikazana sta primera dveh različnih vrst ciljev: homogeni in nehomogeni cilji. Za določitev razdalje med izstrelkom in ciljem ob detonaciji je bil uporabljen pristop navideznega izhodišča. Za verifikacijo rezultatov programa CUMUL je bilo preizkušenih 20 vzorcev oblikovanega polnila. Izračuni programa CUMUL so primerjani z rezultati eksperimentov, ki vključujejo študijo kota pri vrhu plašča in vpliv razdalje med izstrelkom in ciljem ob detonaciji na penetracijo 64-milimetrske protitankovske rakete z oblikovanim polnilom.

Iz primerjave med rezultati eksperimentov in programa CUMUL sledi, da se rezultati programa CUMUL dobro ujemajo z eksperimenti.

V modelu in računalniški kodi so vključeni vsi nedavno razviti modeli za različne faze mehanizmov in penetracije bojnih glav, ki omogočajo edinstveno določanje vplivov različnih konstrukcijskih dejavnikov na zmogljivost izstrelka z oblikovanim polnilom. Koda CUMUL je torej zelo zmogljivo orodje za snovanje bojnih glav z oblikovanim polnilom.

Ključne besede: bojna glava z oblikovanim polnilom, curek oblikovanega polnila, zasnova bojne glave, računalniška koda, penetracija

*Naslov avtorje za dopisovanje: Univerza v Beogradu, Fakulteta za strojništvo, Kraljice Marije 16, Beograd, Srbija, dmickovic@mas.bg.ac.rs

SI 79

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 80

Prejeto: 2011-12-20, sprejeto: 2012-05-04 © 2012 Strojniški vestnik. Vse pravice pridržane.

Vpliv dimenzij delov in velikosti toleranc na sprožilno karakteristiko Macko, M. – Ilić, S. – Jezdimirović, M. Martin Macko1,* - Slobodan Ilić2 – Mirko Jezdimirović2 1 Univerza za obrambo, Brno, Češka republika 2 Univerza za obrambo, Vojaška akademija, Srbija

Namen članka je objava znanja o negativnem vplivu dimenzij delov in velikosti toleranc na sprožilno karakteristiko ročnega strelnega orožja. Sprožilna karakteristika podaja odvisnost sprožilne sile in sprožilnega kota.

Problem je izbira pravih dimenzij in toleranc sprožilca za doseganje ergonomske sprožilne karakteristike.

Natančnost streljanja je odvisna od več dejavnikov: položaja ustja cevi med streljanjem, velikosti in vrste izstrelka ter atmosferskih pogojev, še zlasti pa od odmikov sprožilnega mehanizma in uravnoteženja sil. Povezava med sprožilnim mehanizmom in strelcem izhaja iz tega, da sila kazalca med proženjem vpliva na sprožilec in tako spreminja položaj ustja cevi, kar izhaja iz notranjih sil in momentov sprožilnega mehanizma. Sprožilna sila povzroči premik ustja cevi, strelec pa skuša z ustrezno reakcijo ohraniti položaj cevi v smeri namerilne črte. Neustrezna sprožilna karakteristika vpliva na natančnost streljanja, spremeniti pa jo je mogoče z ustrezno izbiro dimenzij in z razmestitvijo posameznih komponent. Cilji so doseženi z analizo in simulacijo s pomočjo matematičnega modela delov sprožilnega mehanizma.

V članku je uporabljen analitični pristop. Z geometrijsko analizo delov sprožilnega mehanizma je bil ustvarjen matematični model, ki omogoča simulacijo procesa proženja. Teoretični okvir članka je mogoče opisati kot sistem smernic za reševanje problemov pri snovanju sprožilnih mehanizmov ročnega strelnega orožja. Enako metodologijo je mogoče uporabiti tudi pri drugih sprožilnih procesih v sistemih, sestavljenih iz človeka in stroja.

Ugotovljeno je bilo, da ima sprožilna sila v vsakem trenutku procesa proženja drugačno velikost in smer, kar negativno vpliva na položaj ustja cevi med streljanjem. Ena glavnih nalog konstruktorja je doseganje optimalne sprožilne karakteristike s pravo izbiro dimenzij, položajev in toleranc delov sprožilnega mehanizma, ki zagotavlja sprostitev udarne igle in primerno sprožilno karakteristiko za strelca.

Raziskava, ki je opisana v tem članku, je osredotočena na sprožilne mehanizme ročnega strelnega orožja, pristop pa je primeren tudi za ugotavljanje vpliva človeka pri proženju mehanizmov strojev drugih vrst.

Novost tega dela je v snovanju sprožilnih mehanizmov pri konstrukciji ročnega strelnega orožja. Pri tem je treba uskladiti gibanja delov sprožilca za ergonomsko sprožilno karakteristiko. Neustrezna kombinacija dimenzij in toleranc delov povzroči neergonomsko sprožilno karakteristiko, ki strelca med proženjem moti. Konstruktorji danes analizirajo in sintetizirajo tolerance v fazi preliminarne konstrukcije mehanizma. Problem je mogoče reševati samodejno z različno programsko opremo ali z analitično obravnavo glavnih parametrov, ki določajo ciljno funkcijo. Takšen pristop pa ponuja le omejene možnosti doseganja ergonomskih sprožilnih karakteristik.

Z uporabo posebne programske opreme za simulacijo sprožilcev drugih mehanizmov je mogoče pridobiti informacije o vseh parametrih, ki vplivajo na funkcijo proženja, torej ne samo o velikosti, tolerancah in položaju, temveč tudi o silah, koeficientih trenja itd.

Na ta način se upošteva tudi trenutni zamik mehanizma, medtem ko CAD-programska oprema ponuja samo analizo ali sintezo toleranc.

Ključne besede: dimenzije, tolerance, ročno strelno orožje, natančnost, sprožilni mehanizem, sprožilna karakteristika

SI 80

*Naslov avtorja za dopisovanje: Univerza za obrambo, Kounicova 65, 66210 Brno, Češka republika, martin.macko@unob.cz

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 81

Prejeto: 2011-12-20, sprejeto: 2012-05-18 © 2012 Strojniški vestnik. Vse pravice pridržane.

Preliminarne preiskave nove generacije oklepne pločevine za lahka oklepna vozila Bernetič, J. – Vuherer, T. – Marčetič, M. – Vuruna, M. Jure Bernetič1,* – Tomaž Vuherer2 – Matjaž Marčetič1 – Mladen Vuruna3 1 Acroni Jesenice, d.o.o., Slovenija 2 Univerza v Mariboru, Fakulteta za strojništvo, Slovenija 3 Univerza za obrambo, Vojaška akademija v Beogradu, Srbija

V podjetju Acroni je bilo razvito novo jeklo PROTAC 500. Prvi preliminarni rezultati preizkušanja mehanskih lastnosti jekla so nakazali možnost uporabe tega jekla za lahka bojna oklepna vozila. Preizkušanje se je nadaljevalo z namenom optimizacije parametrov toplotne obdelave jekla za doseganje optimalnega razmerja med napetostjo tečenja in natezno trdnostjo, ter dobro zaščito pred izstrelki iz lahkega orožja. V ta namen smo se odločili za raziskavo primernosti jekla za oklepe lahkih bojnih vozil. K pisanju prispevka so nas spodbudili preliminarni rezultati preizkušanja balistične odpornosti oklepnega jekla v treh različnih toplotno obdelanih stanjih. Nivo balistične zaščite našega jekla v določenih segmentih celo presega konkurenčna jekla, ki so trenutno na voljo na tržišču.

Za novo razvito jeklo je bilo treba pridobiti rezultate nateznega preizkusa. Izvedeni so bili natezni preizkusi pri sobni temperaturi na cilindričnih preizkušancih premera 5 mm. Rezultati so pokazali, da dobimo največjo natezno trdnost v izhodiščnem stanju (stanje A). Če jeklo popuščamo pri temperaturi 220 °C (Stanje B) ali 280 °C (stanje C) tri ure, se njegova natezna trdnost zmanjša, napetost tečenja pa se poveča. Pri balistični zaščiti, kjer mora jeklo ustaviti projektil, sta ključna trdnost in sposobnost plastične deformacije jekla – torej razmerje (Rm/Rp0.2). Slednja je pomembna pri zaustavljanju projektila, saj se s plastično deformacijo absorbira energija projektila. Rezultati kažejo, da je najugodnejše razmerje (Rm/Rp0.2) doseženo pri stanju A. S popuščanjem se zmanjša trdota jekla, ki se je zmanjšala iz 569 HV10 pri stanju A na 533 HV10 pri stanju B in na 525 HV10 pri stanju C. Udarna žilavost jekla je bila preizkušena s Charpyjevim kladivom. Pri preizkusu se beležijo podatki o sili in času, posredno pa se meri tudi energija, ki se absorbira zaradi lomljenja Charpyjevega preizkušanca. S pomočjo oblike diagrama in magnetnega senzorja, ki zazna, kdaj se pri preizkusu začne širiti razpoka, lahko energijo za lom Charpyjevega preizkušanca razdelimo na energijo za nastanek razpoke in energijo za širjenje razpoke. Ti podatki in oblike diagramov sila-pot kladiva veliko povedo o vedenju jekla, ki je obremenjeno z veliko hitrostjo deformacije. Izkazalo se je, da je največja udarna žilavost zabeležena v stanju B, vendar razlike med stanji niso velike.

Za odločitev o primernosti jekla za oklepe lahkih bojnih vozil je najpomembnejši preizkus o balistični zaščiti po standardu STANAG 4569. Preizkusi so bili izvedeni na vojaškem poligonu pri Beogradu. Pri preizkušanju se meri hitrost jeklenega izstrelka 7.62×39 mm API BZ iz preizkuševalne cevi, ki ustreza standardu STANAG 4569 za uporabo pri testiranju. Pri preizkušanju je obvezna uporaba takšne cevi, saj uporaba puške AK 47 ne zagotavlja optimalnih rezultatov. Pri preizkusu se meri hitrost jeklenega izstrelka (62±1) HRC, ki ga z oddaljenosti 30 m izstrelimo pravokotno na ploščo iz preizkušanega jekla. Projektil prileti v ploščo, ki jo preizkušamo, s hitrostjo približno 700 m/s. Hitrost projektila se meri z dvojno optično zaveso tik pred preizkusno ploščo. Rezultati so pokazali, da dobimo najboljše rezultate pri stanju A. Noben projektil ni prebil plošče in pri nobenem tudi niso bile ugotovljene razpoke na zadnji strani plošče, le na enem mestu je bilo zaznati večjo plastično deformacijo.

Najslabši rezultati balistične zaščite so pri stanju C, kjer je bila v dveh primerih ugotovljena popolna penetracija projektila, to pa pomeni, da jeklo v stanju C ni primerno za protibalistično zaščito Raziskava je pokazala, da je za balistične lastnosti materiala pomembna interakcija natezne trdnosti, trdote, duktilnosti in udarne žilavosti materiala. Optimalna kombinacija teh lastnosti je odločilna za zagotovitev preizkušanja ravni balistične zaščite jekla PROTAC 500. Trenutno je to le še preliminarna raziskava, za boljše razumevanje in statistično obdelavo rezultatov pa je treba izvesti več balističnih preizkusov. V literaturi je sicer le malo člankov, ki bi balistične rezultate povezali z rezultati preizkušanja s Charpyjevim kladivom.

V prihodnje bi bilo treba mesta zadetkov projektilov še metalografsko pregledati ter ugotoviti stopnje plastične deformacije materiala.

Ključne besede: oklepna pločevina, natezna trdnost, napetost tečenja, udarna žilavost, trdota, balistična zaščita *Naslov avtorje za dopisovanje: Acroni, d.o.o., Cesta Borisa Kidriča 44, 4270 Jesenice, Slovenija, jure.bernetic@acroni.si

SI 81

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 82

Prejeto: 2011-12-20, sprejeto: 2012-04-24 © 2012 Strojniški vestnik. Vse pravice pridržane.

Eksperimentalna raziskava zvarnih spojev visokotrdnostnih konstrukcijskih jekel Ismar, H. – Burzic, Z. – Kapor, N.J. – Kokelj, T. Hajro Ismar1,*– Zijah Burzic2 – Nenad J.Kapor3 – Tugomir Kokelj4 1 Univerza v Sarajevu, Fakulteta za strojništvo, Bosna in Hercegovina 2 Vojno-tehnični institut, Beograd, Srbija 3 Univerza v Beogradu, Fakulteta za strojništvo, Srbija 4 Univerza za obrambo, Vojaška akademija, Beograd, Srbija

Žilavost postaja z razvojem področja lomne mehanike vse pomembnejša mehanska lastnost materialov, kakor tudi konstrukcijska spremenljivka. Žilavost je še posebej pomemben parameter pri novejših konstrukcijskih materialih kot so visokotrdnostna jekla. Ker se visokotrdnostna jekla uporabljajo predvsem v različnih varjenih konstrukcijah, postaja vse pomembnejše tudi vrednotenje neujemanja lastnosti zvarnih spojev, vključno z žilavostjo. V članku so predstavljeni rezultati raziskave porazdelitve in neujemanja udarne in kvazistatične žilavosti pri zvarnih spojih delov iz jekla visoke trdnosti.

Značilne heterogene cone zvarnih spojev so bile ugotovljene s pomočjo preizkusov in simulacij varjenja.

Soležni zvarni spoji so bili izvedeni s pomočjo postopka MIG-varjenja dveh izbranih visokotrdnostnih konstrukcijskih jekel S690QL in S890QL. Ob upoštevanju dobro znanega dejstva, da je najšibkejši del zvara grobozrnata toplotno vplivana cona (CG-HAZ), so bili pripravljeni dodatni preizkusi na osnovi simulacije toplotnih ciklov varjenja z največjo temperaturo 1300 °C in časom hlajenja Dt8/5 je 6 do 8 s, kar so ocenjeni parametri pri realnih zvarih. Zato so bile eksperimentalno preizkušene številne lastnosti osnovnega materiala (BM) in zvara (WM), kakor tudi toplotno vplivane cone (HAZ): omejena kemična sestava (ogljikov ekvivalent), trdota, natezna in udarna žilavost, ter kvazistatična žilavost. Na ta način so bili pridobljeni obsežni podatki o mehanskih lastnostih, ki dajejo dovolj podatkov za nadaljnjo regresijsko analizo in ugotavljanje razmerij med obravnavanimi lastnostmi.

Podobno metodologijo in koncept analize (razmerja) podpirajo tudi številni raziskovalci v novejši literaturi.

Razen natančnega ovrednotenja mehanskih lastnosti so najpomembnejši rezultati pridobljeni v zvezi s porazdelitvijo splošnih lastnosti po srednjici zvarnega spoja, ugotovljena pa so bila tudi razmerja, ki so natančnejša in zanesljivejša od obstoječih podatkov v literaturi, namenjenih bolj splošni uporabi. V splošnem so bili zvari na obeh jeklih v stanju navzdolnjega neujemanja trdote in trdnosti v območju od 0,98 do 0,99, in z razmerjem žilavosti CG-HAZ, realne HAZ in WM glede na BM v razponu od 0,32 do 0,96. Najšibkejša žilavost je bila ugotovljena v območju CG-HAZ (do 0,32).

Izsledki in končne vrednosti ugotovljenih razmerij seveda veljajo samo za zvarne spoje visokotrdnostnih konstrukcijskih jekel z razredom trdnosti osnovnega materiala Rp0,2 je 690 do 890 MPa in v območju debelin BM od 20 do 30 mm. Tudi dejstvo, da so bili zvarni spoji ustvarjeni s postopkom talilnega varjenja (MIG), je treba upoštevati kot omejitev pri uporabi predstavljenih razmerij. Iz teh omejitev izhajajo določene zamisli o prihodnjih raziskavah v zvezi s pridobivanjem in uporabo prikazanih razmerij, ki vključujejo vsaj vpliv temperature, širši razpon debelin, druge varilne postopke in celo druge razrede trdnosti jekla.

Glavni prispevek raziskave je določitev razmerij med različnimi mehanskimi lastnostmi, zlasti udarno in kvazistatično žilavostjo, ki lahko pomaga pri poenostavljanju inženirskih napovedi. Rezultati bodo še posebej zanimivi za raziskovalce, ki ne razpolagajo s sofisticirano opremo in specializiranim osebjem za preizkušanje lomne mehanike. Predstavljeni splošni eksperimentalni postopek in rezultati prinašajo več zaupanja in zanesljivosti pri prihodnjih vrednotenjih zvarnih spojev, bodisi za kvalifikacijo varilnih postopkov, numerične simulacije varjenih konstrukcij iz različnih materialov, ali pa za splošno ocenjevanje integritete konstrukcij.

Ključne besede: visokotrdnostno jeklo, zvarni spoji, žilavost, porazdelitev, razmerja

SI 82

*Naslov avtorja za dopisovanje: Univerza v Sarajevu, Fakulteta za strojništvo, Vilsonovo šetalište 9, Sarajevo, Bosna in Hercegovina, hajro@mef.unsa.ba

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 83-86 Osebne objave

Doktorske disertacije, znanstvena magistrska dela, specialistična dela, diplomske naloge

DOKTORSKE DISERTACIJE Na Fakulteti za strojništvo Univerze v Ljubljani so z uspehom obranili svojo doktorsko disertacijo: dne 17. maja 2012 Matej ŽVOKELJ z naslovom: »Vpliv malocikličnih utrujenostnih poškodb na obratovanje v vrtljivih kotalnih zvezah« (mentor: prof. dr. Ivan Prebil, somentor: doc. dr. Samo Zupan); Odpoved funkcije počasi vrtečih se kotalnih ležajev velikih mer, uporabljenih v raznih kritičnih vrtljivih kotalnih zvezah, praviloma povzroči dolgotrajne in drage zastoje, obenem pa predstavlja potencialno nevarnost za prisotno osebje. S ciljem zaznavanja predvsem kotalno stičnih utrujenostnih poškodb, kot dominantnih poškodb ležajev, spremljanja njihove rasti ter ugotavljanja njihovega vpliva na obratovanje vrtljivih kotalnih zvez, v katere so ti ležaji vgrajeni, so razvite nove večločljivostne multivariatne statistične nadzorne metode. Razvite metode združujejo multivariatne metode spremljanja stanja (PCA (metoda glavnih osi), KPCA (jedrna metoda glavnih osi), KICA (jedrna metoda neodvisnih osi)), ki nam ponujajo mehanizem, s katerim lahko pridobimo in strukturiramo koristno informacijo iz visoko dimenzionalne baze podatkov z ansambelsko metodo empirične dekompozicije (EEMD), ki signale adaptivno razstavi na različne časovne skale. Metode, ki smo jih s skupnim imenom poimenovali EEMDosnovane multivariatne statistične monitoring metode (metode spremljanja stanja) ter označili s kratico EEMD-MSMM, poleg same detekcije poškodbe ponujajo tudi mehanizem odstranjevanja šuma ter obenem, v kombinaciji z metodo ovojnice, orodje namenjeno diagnostiki. Učinkovitost predlaganih metod EEMD-MSMM je bila preverjena na nizu eksperimentalnih meritev, opravljenih na namensko zgrajenem laboratorijskem preizkuševališču, opremljenim s kompleksnim merilno-krmilnim sistemom, pri čemer so bile poškodbe simulirane, opravljen pa je bil tudi trajnostni preizkus. Za nosilca informacij o stanju ležaja so bile uporabljene vibracije, akustična emisija, relativni premik med ležajnima obročema, napetosti v priključni konstrukciji in vrtilni upor ležaja, merjen s pomočjo namensko izdelanega upogibnega senzorja in električnega toka, ki ga za pogon vrtljive kotalne zveze troši pogonski elektromotor. Sposobnost zaznavanja tudi najmanjših lokalnih poškodb kotalnega ležaja kaže na to, da izbrane procesne spremenljivke, ki jih spremljamo

in zajemamo s kompleksnim merilnim sistemom preizkuševališča, nosijo dovolj informacij o stanju ležaja ter da lahko s pomočjo predlaganih metod EEMD-MSMM z visoko zanesljivostjo zaznavamo poškodbe v tovrstnih zvezah; dne 23. maja 2012 Matej TADINA z naslovom: »Karakterizacija vibracij poškodovanega krogličnega ležaja pri spreminjajoči vrtilni frekvenci« (mentor: prof. dr. Miha Boltežar); Delo obravnava izboljšan matematični model enorednega krogličnega ležaja s poškodbami za simuliranje vibracij, ki se pojavijo pri zagonu. V razvitem numeričnem modelu ležaja je predstavljeno, da ima notranji obroč le dve prostostni stopnji, zunanji obroč pa je prožen v radialni smeri. Zunanji obroč je modeliran v sklopu teorije končnih elementov in zanj je uporabljen ukrivljeni končni element. V modelu je upoštevana centrifugalna sila na kroglice in radialna zračnost ležaja. Kontaktne razmere so modelirane v sklopu Hertzeve kontaktne teorije. V modelu so upoštevane lokalne poškodbe na tekalnih površinah ležaja. Geometrija poškodb na notranjem in zunanjem obroču je popisana z Gaussovo funkcijo, medtem ko je na poškodba kroglice modelirana s krogelnim odsekom. Razviti model ležaja je uporabljen za simuliranje vibracij točkovno poškodovanih ležajev pri zagonu. Na osnovi simuliranih signalov so izbrani primerni parametri za metodo ovojnice in HilbertHuangovo transformacijo za identifikacijo napak na ležajih. S tako določenimi parametri sta metodi validirani na eksperimentalno pomerjenih vibracijah poškodovanih ležajev; dne 28. maja 2012 Žiga ZADNIK z naslovom: »Matrika funkcij in funkcionalnosti izdelka v razvojno konstrukcijskem procesu« (mentor: prof. dr. Jožef Duhovnik, somentor: izr. prof. dr. Jože Tavčar); Delo s teoretičnega in praktičnega vidika obravnava dejavnike, ki vplivajo na razvoj novega izdelka v okviru faze zasnove zgodnjega razvojnokonstrukcijskega procesa. Na podlagi dosedanjih metod je prepoznana in predstavljena nova metoda »Matrike funkcij in funkcionalnosti – MFF«, ki ne vključuje osnovne konstrukterske intuicije, je matematično zasnovana, zajema abstraktne smernice in omogoča sprotno samokontrolo ob ponovljivih rezultatih. Osnovana je na funkcijskih zahtevah in funkcionalnostih. Izdelano in opisano je praktično računalniško okolje, ki omogoča uporabo nove metode neodvisno od lokacije. Tako metoda kot aplikacija SI 83

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 83-86

sta preizkušeni preko implementacije raznovrstnih izdelkov; dne 31. maja 2012 Andrej SVETE z naslovom: »Vpliv tokovnih pulzacij na merilno točnost merilnikov pretoka« (mentor: izr. prof. dr. Ivan Bajsić, somentor: doc. dr. Jože Kutin); Delo predstavlja razvoj preizkusnega merilnega sistema z vgrajenim generatorjem tokovnih pulzacij vode za eksperimentalno proučevanje vpliva tokovnih pulzacij na merilnike pretoka. Mehanska izvedba merilnega sistema z vgrajenim membranskim generatorjem pulzacij in razteznima posodama je bila razvita s pomočjo matematičnega modeliranja celotnega merilnega sistema z uporabo metode karakteristik. Lastnosti generatorja tokovnih pulzacij vode so bile eksperimentalno potrjene z uporabo spektralne analize generiranih tokovnih pulzacij, ki so bile izmerjene z uporabo dušilne merilne metode.

Razviti generator pulzacij je bil uporabljen za proučevanje dinamičnih zmogljivosti hidravličnega Wheatstonovega merilnega mostiča. Za ta namen smo z nadgradnjo statičnega fizikalno-matematičnega modela, kjer smo upoštevali vplive stisljivosti in vztrajnosti tekočine, razvili tudi dinamični model merilnika. Ugotovljeno je bilo, da je merilnik zaradi linearne merilne značilnice neobčutljiv na korenske merilne pogreške, kar ne velja za standardno dušilno merilno metodo. Hkrati frekvenčna značilnica merilnika kaže tipično resonanco, katere vrednost je odvisna od tekočinskih lastnosti in dimenzij mostiča.

Rezultati matematičnega modeliranja kažejo dobro ujemanje z rezultati eksperimentalne analize. * Na Fakulteti za strojništvo Univerze v Mariboru je z uspehom obranil svojo doktorsko disertacijo: dne 10. maja 2012 Miran KAPITLER z naslovom: »Numerična analiza pogojev zgorevanja odpadkov in optimizacija zgorevalnega prostora kurilne naprave z rešetko« (mentor: prof. dr. Niko Samec); Proces zgorevanja, ki se odvija v kurilnih napravah in uporablja mestne komunalne odpadke kot gorivo, zahteva natančno razumevanje tega fenomena.

Ta proces je odvisen od mnogih vhodnih parametrov, kot je kvalitativna analiza mestnih komunalnih odpadkov, letni čas, hitrost vstopnega primarnega in sekundarnega zraka, ter od izhodnih parametrov, kot je temperatura ali masno razmerje produktov zgorevanja na izstopu. Upravljanje s spremenljivostjo in medsebojno odvisnostjo teh parametrov je v praksi lahko zelo oteženo, saj moramo zagotoviti optimalno zgorevanje z minimalnimi emisijami polutantov že v projektni fazi. Z uporabo računalniške dinamike SI 84

tekočin smo proučevali realno kurilno napravo z zgorevanjem na rešetki s programskim paketom ANSYS CFX v okolju WORKBENCH 2. V nalogi smo uporabili variabilne robne pogoje vhodnih parametrov, ki bazirajo na rezultatih drugih avtorjev, in uporabili turbulentne, zgorevalne in sevalne modele ter modele za prenos toplote. Nadalje smo optimirali obratovalne pogoje obstoječe kurilne naprave in geometrijske parametre nove s pomočjo ciljno usmerjene optimizacije, tridimenzionalno napovedali in slikovno predstavili čas zadrževanja, temperaturna in hitrostna polja, tokovnice, sledili delcem letečega pepela, poljam koncentracij reaktantov in produktov zgorevanja ter formiranju dušikovih oksidov. Cilj optimizacije je ugotoviti vrednost posameznega vhodnega parametra, pri katerem obstoječa naprava dosega optimalne ali kritične − škodljive obratovalne pogoje oziroma optimalne dimenzije nove.

Odvisnost med vhodnimi in izhodnimi parametri, ki jih definiramo in predstavljajo specifične pokazatelje popolnosti zgorevanja, smo prikazali v odzivnih diagramih, stopnjah občutljivosti posameznega parametra, histogramih in linearnih korelacijskih matrikah. Ta spoznanja nam zagotavljajo pomoč pri upravljanju kurilne naprave in preprečevanju kritičnih režimov obratovanja pri neugodnih spremembah obratovanja ter pri snovanju novih.

Prikazan znanstveni pristop omogoča CFD analizo, numerično optimizacijo obratovalnih pogojev in zgorevalnega prostora že v sami projektni fazi snovanja bodoče kurilne naprave, kar nam omogoča hitrejši in učinkovitejši razvoj izdelka s pričakovano kakovostjo in obratovalno zanesljivostjo ter občutno znižuje stroške raziskav in daje prednost pred konkurenco.

ZNANSTVENA MAGISTRSKA DELA Na Fakulteti za strojništvo Univerze v Ljubljani sta z uspehom zagovarjala svoje magistrsko delo: dne 17. maja 2012 Janez LAP z naslovom: »Obvladovanje naročila v distribuiranem okolju« (mentor: prof. dr. Alojzij Sluga); dne 18. maja 2012 Blaž BAJŽELJ z naslovom: »Nadzor nastanka radijev odrezkov pri struženju z visokotlačnim dovodom hladilno-mazalnega sredstva« (mentor: prof. dr. Janez Kopač, somentor: doc. dr. Davorin Kramar).

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 83-86

SPECIALISTIČNO DELO Na Fakulteti za strojništvo Univerze v Mariboru sta z uspehom zagovarjala svoje specialistično delo: dne 6. aprila 2012 Aleš SEMPRIMOŽNIK z naslovom: »Razvoj superabrazivnega brusnega orodja v hibridni vezi« (mentor: prof. dr. Ivan Anžel); dne 9. maja 2012 Aleksander SEDOVŠEK z naslovom: »Konstrukcija okvirja kuhalne enote aparata za napitke« (mentor: prof. dr. Zoran Ren).

DIPLOMIRALI SO Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv univerzitetni diplomirani inženir strojništva: dne 7. maja 2012: Georg HALUŽAN z naslovom: »Avtomatizacija strege procesa kontrole trdote vijakov« (mentor: izr. prof. dr. Niko Herakovič); dne 24. maja 2012: Dejan BOGATAJ z naslovom: »Energijska in eksergijska analiza delovanja Stirlingovega motorja na biomaso, inštaliranega v stavbi« (mentor: prof. dr. Vincenc Butala Somentor: doc. dr. Uroš Stritih); Jernej BRATUŠA z naslovom: »Uplinjevalnik lesne biomase z lebdečo plastjo« (mentor: izr. prof. dr.

Andrej Senegačnik); Blaž ŠMERC z naslovom: »Alternativni načini ogrevanja stanovanjskih in javnih zgradb večjega naselja« (mentor: prof. dr. Alojz Poredoš); Peter ENIKO z naslovom: »Statistični nadzor procesa izdelave hidravličnih blokov« (mentor: doc. dr. Davorin Kramar, somentor: prof. dr. Janez Kopač); Marko POGAČAR z naslovom: »Sistem za regulacijo temperature laserskih diod« (mentor: prof. dr. Janez Diaci, somentor: doc. dr. Rok Petkovšek); Jaka PRIBOŠEK z naslovom: »Sistem za lokalizacijo in sledenje kirurških instrumentov pri minimalno invazivnih operacijah« (mentor: prof. dr.

Janez Diaci); dne 29. maja 2012: Uroš JEŠE z naslovom: »Razgradnja zdravilnih učinkovin s pomočjo kavitacije« (mentor: doc. dr.

Matevž Dular, somentor: prof. dr. Branko Širok); Boštjan JURJEVČIČ z naslovom: »Analiza algoritmov za izračun stisljivosti zemeljskega plina v plinovodnem sistemu« (mentor: prof. dr. Branko Širok); Jaka ROVAN z naslovom: »Temperaturni učinki pri rasti in kolapsu kavitacijskega mehurčka« (mentor: doc. dr. Matevž Dular, somentor: prof. dr. Branko Širok);

Michiel Van HERZEELE z naslovom: »Določitev parametrov pogonskega sklopa v realnih voznih ciklih« (Evaluation of powertrain parameters during real world driving cycles), (mentor: izr. prof. dr.

Tomaž Katrašnik). * Na Fakulteti za strojništvo Univerze v Mariboru sta pridobila naziv univerzitetni diplomirani inženir strojništva: dne 24. maja 2012: Andrej DOLINAR z naslovom: »Električni vlačilec za športna letala« (mentor: doc. dr. Aleš Belšak, somentor: izr. prof. dr. Miran Ulbin); Nejc MARČIČ z naslovom: »Inženirsko oblikovanje nove kopalniške armature za Mariborsko Livarno Maribor« (mentor: izr. prof. Vojmir Pogačar, somentor: doc. dr. Andrej Skrbinek); Denis PRKIČ z naslovom: »Projekt razvoja novega energetskega okna za bivalne enote v podjetju Arcont IP d.o.o.« (mentor: doc. dr. Iztok Palčič, somentor: prof. dr. Riko Šafarič); Aljaž ZUPANC z naslovom: »Prenos profila DIN 1570 na novo linijo valjanja« (mentor: prof. dr. Nenad Gubeljak, somentor: dr. Miha Kovačič). * Na Fakulteti za strojništvo Univerze v Ljubljani so pridobili naziv diplomirani inženir strojništva: dne 10. maja 2012: Matej JAKI z naslovom: »Vpliv terena in ovir na pot letala med letom na rezervno letališce« (mentor: doc. dr. Viktor Šajn, pred. Miha Šorn); Uroš JORDAN z naslovom: »Mikrovalovno vakuumsko sušenje medu« (mentor: prof. dr. Iztok Golobič); Urban TAJNŠEK z naslovom: »Razvoj naprave za preskušanje trdnosti zobatih obročev« (mentor: prof. dr. Marko Nagode); Boštjan VRCON z naslovom: »Prevzemni preizkus prezračevalnega sistema« (mentor: izr. prof. dr. Ivan Bajsić); dne 11. maja 2012: Bojan ARH z naslovom: »Prilagodljiva vpenjalna priprava za velike obdelovance« (mentor: prof. dr.

Janez Kopač); Noka KUNEJ z naslovom: »Vpliv mehanske predpriprave sadja in zelenjave na proces sočenja« (mentor: doc. dr. Henri Orbanič, somentor: prof. dr.

Mihael Junkar); Jure POTRPIN z naslovom: »Primerjava izmerjenih in numeričnih rezultatov na aerodinamične lastnosti aeroprofila FX 63-137 pri majhnih SI 85

Strojniški vestnik - Journal of Mechanical Engineering 58(2012)6, SI 83-86

Reynoldsovih številih« (mentor: izr. prof. dr. Tadej Kosel); Luka ŠTRUS z naslovom: »Prihodnost upravljanja zračnega prometa - SESAR« (mentor: izr. prof. dr. Tadej Kosel, somentor: pred. mag. Andrej Grebenšek). * Na Fakulteti za strojništvo Univerze v Mariboru so pridobili naziv diplomirani inženir strojništva: dne 24. maja 2012: Blaž ANTLOGA z naslovom: »Razvoj merilne proge za določanje karakteristik toplotnih prenosnikov v laboratoriju HZA podjetja Gorenje« (mentor: prof. dr. Aleš Hribernik, somentor: doc. dr. Matjaž Ramšak); Aleš JESENIČNIK z naslovom: »Konstrukcija transportnega sistema za avtomatsko tehtanje polizdelkov« (mentor: prof. dr. Iztok Potrč, somentor: izr. prof. dr. Tone Lerher);

SI 86

Dragan JOVIĆ z naslovom: »Posodobitev numerično krmiljenega obdelovalnega stroja« (mentor: izr. prof. dr. Ivan Pahole, somentor: doc. dr.

Mirko Ficko); Simon KOZIKAR z naslovom: »Koncipiranje in snovanje prijemalne naprave za vrtanje motorskih gredi« (mentor: izr. prof. dr. Stanislav Pehan); Dejan KUNČNIK z naslovom: »Transportni sistemi za polnjenje pretočnih regalov« (mentor: prof. dr. Iztok Potrč); Kristijan TADIČ z naslovom: »Optimizacija proizvodnega procesa titan izpušnih sistemov za motorno kolo« (mentor: doc. dr. Marjan Leber, somentor: izr. prof. dr. Stanislav Pehan); Matjaž TREBOVŠEK z naslovom: »Obdelovalni stroji v orodjarstvu« (mentor: doc. dr. Mirko Ficko); Matjaž TUŠAK z naslovom: »Konstruiranje priprave za transport nosilca gosenic žerjava« (mentor: doc. dr. Janez Kramberger).

Strojniški vestnik – Journal of Mechanical Engineering (SV-JME) Aim and Scope The international journal publishes original and (mini)review articles covering the concepts of materials science, mechanics, kinematics, thermodynamics, energy and environment, mechatronics and robotics, fluid mechanics, tribology, cybernetics, industrial engineering and structural analysis.

The journal follows new trends and progress proven practice in the mechanical engineering and also in the closely related sciences as are electrical, civil and process engineering, medicine, microbiology, ecology, agriculture, transport systems, aviation, and others, thus creating a unique forum for interdisciplinary or multidisciplinary dialogue.

The international conferences selected papers are welcome for publishing as a special issue of SV-JME with invited co-editor(s).

Editor in Chief Vincenc Butala University of Ljubljana Faculty of Mechanical Engineering, Slovenia Guest Editor Momčilo Milinović University of Belgrade Faculty of Mechanical Engineering, Serbia Technical Editor Pika Škraba University of Ljubljana Faculty of Mechanical Engineering, Slovenia Editorial Office University of Ljubljana (UL) Faculty of Mechanical Engineering SV-JME Aškerčeva 6, SI-1000 Ljubljana, Slovenia Phone: 386-(0)1-4771 137 Fax: 386-(0)1-2518 567 E-mail: info@sv-jme.eu, http://www.sv-jme.eu Print Tiskarna Knjigoveznica Radovljica, printed in 480 copies Founders and Publishers University of Ljubljana (UL) Faculty of Mechanical Engineering, Slovenia University of Maribor (UM) Faculty of Mechanical Engineering, Slovenia Association of Mechanical Engineers of Slovenia

http://www.sv-jme.eu

58 (2012) 6

Chamber of Commerce and Industry of Slovenia Metal Processing Industry Association

Since 1955

Strojniški vestnik Journal of Mechanical Engineering

Cover: FEM simulated time dependent stress field on chassis of 6×6 light armoured vehicle during demanding terrain mission.

an Bondžulić, Bojan Zrnić, Aleksandar Kari, Goran Dikić: tal Data Analysis of Moving Targets Echoes Observed by

omir Janković, Nebojša Nikolić: lays Design Criteria

ilo Milinović, Danijela Randjelović: Enhancement of Infrared Detectors by Plasmon Resonance ductive Oxide Nanoparticles

Dejan Micković, Predrag Elek, Dragana Jaramaz,

Charge Warhead Design

dan Ilić, Mirko Jezdimirović: rt Dimensions and Tolerance Size to Trigger

ž Vuherer, Matjaž Marčetič, Mladen Vuruna: arch on New Grade of Steel Protective Material ed Vehicles

urzic, Nenad J. Kapor, Tugomir Kokelj: tigation of High-Strength Structural Steel Welds

Journal of Mechanical Engineering - Strojniški vestnik

Damir Jerković, Olivera Jeremić, Mitar Kovač: imulation Testing of Flight Spin Stability for Small Caliber

year

no. 6 2012 58

volume

Image courtesy: Chair of Modelling in Engineering Sciences and Medicine, Faculty of Mechanical Engineering, University of Ljubljana

International Editorial Board Koshi Adachi, Graduate School of Engineering,Tohoku University, Japan Bikramjit Basu, Indian Institute of Technology, Kanpur, India Anton Bergant, Litostroj Power, Slovenia Franci Čuš, UM, Faculty of Mech. Engineering, Slovenia Narendra B. Dahotre, University of Tennessee, Knoxville, USA Matija Fajdiga, UL, Faculty of Mech. Engineering, Slovenia Imre Felde, Bay Zoltan Inst. for Mater. Sci. and Techn., Hungary Jože Flašker, UM, Faculty of Mech. Engineering, Slovenia Bernard Franković, Faculty of Engineering Rijeka, Croatia Janez Grum, UL, Faculty of Mech. Engineering, Slovenia Imre Horvath, Delft University of Technology, Netherlands Julius Kaplunov, Brunel University, West London, UK Milan Kljajin, J.J. Strossmayer University of Osijek, Croatia Janez Kopač, UL, Faculty of Mech. Engineering, Slovenia Franc Kosel, UL, Faculty of Mech. Engineering, Slovenia Thomas Lübben, University of Bremen, Germany Janez Možina, UL, Faculty of Mech. Engineering, Slovenia Miroslav Plančak, University of Novi Sad, Serbia Brian Prasad, California Institute of Technology, Pasadena, USA Bernd Sauer, University of Kaiserlautern, Germany Brane Širok, UL, Faculty of Mech. Engineering, Slovenia Leopold Škerget, UM, Faculty of Mech. Engineering, Slovenia George E. Totten, Portland State University, USA Nikos C. Tsourveloudis, Technical University of Crete, Greece Toma Udiljak, University of Zagreb, Croatia Arkady Voloshin, Lehigh University, Bethlehem, USA President of Publishing Council Jože Duhovnik UL, Faculty of Mechanical Engineering, Slovenia General information Strojniški vestnik – Journal of Mechanical Engineering is published in 11 issues per year (July and August is a double issue).

Institutional prices include print & online access: institutional subscription price and foreign subscription €100,00 (the price of a single issue is €10,00); general public subscription and student subscription €50,00 (the price of a single issue is €5,00). Prices are exclusive of tax.

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ISSN 0039-2480 © 2011 Strojniški vestnik - Journal of Mechanical Engineering. All rights reserved. SV-JME is indexed / abstracted in: SCI-Expanded, Compendex, Inspec, ProQuest-CSA, SCOPUS, TEMA. The list of the remaining bases, in which SV-JME is indexed, is available on the website. The journal is subsidized by Slovenian Book Agency.

Strojniški vestnik - Journal of Mechanical Engineering is also available on http://www.sv-jme.eu, where you access also to papers’ supplements, such as simulations, etc.

Instructions for Authors All manuscripts must be in English. Pages should be numbered sequentially. The maximum length of contributions is 10 pages. Longer contributions will only be accepted if authors provide justification in a cover letter. Short manuscripts should be less than 4 pages. For full instructions see the Authors Guideline section on the journal’s website: http://en.sv-jme.eu/.

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THE FORMAT OF THE MANUSCRIPT The manuscript should be written in the following format: - A Title, which adequately describes the content of the manuscript.

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Acknowledgement of collaboration or preparation assistance may be included before References. Please note the source of funding for the research.

REFERENCES A reference list must be included using the following information as a guide. Only cited text references are included. Each reference is referred to in the text by a number enclosed in a square bracket (i.e., [3] or [2] to [6] for more references). No reference to the author is necessary.

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Journal Papers: Surname 1, Initials, Surname 2, Initials (year). Title. Journal, volume, number, pages, DOI code.

[1] Hackenschmidt, R., Alber-Laukant, B., Rieg, F. (2010). Simulating nonlinear materials under centrifugal forces by using intelligent crosslinked simulations. Strojniški vestnik - Journal of Mechanical Engineering, vol. 57, no. 7-8, p. 531-538, DOI:10.5545/sv-jme.2011.013.

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[2] Groover, M.P. (2007). Fundamentals of Modern Manufacturing. John Wiley & Sons, Hoboken.

Note that the title of the book is italicized.

Chapters in Books: Surname 1, Initials, Surname 2, Initials (year). Chapter title. Editor(s) of book, book title. Publisher, place of publication, pages.

[3] Carbone, G., Ceccarelli, M. (2005). Legged robotic systems. Kordić, V., Lazinica, A., Merdan, M. (Eds.), Cutting Edge Robotics. Pro literatur Verlag, Mammendorf, p. 553-576.

Proceedings Papers: Surname 1, Initials, Surname 2, Initials (year). Paper title. Proceedings title, pages.

[4] Štefanić, N., Martinčević-Mikić, S., Tošanović, N. (2009). Applied Lean System in Process Industry. MOTSP 2009 Conference Proceedings, p.

422-427.

Standards: Standard-Code (year). Title. Organisation. Place.

[5] ISO/DIS 16000-6.2:2002. Indoor Air – Part 6: Determination of Volatile Organic Compounds in Indoor and Chamber Air by Active Sampling on TENAX TA Sorbent, Thermal Desorption and Gas Chromatography using MSD/FID. International Organization for Standardization. Geneva. www pages: Surname, Initials or Company name. Title, from http://address, date of access.

[6] Rockwell Automation. Arena, from http://www.arenasimulation.com, accessed on 2009-09-07.

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58 (2012) 6

Strojniški vestnik Journal of Mechanical Engineering

Since 1955

Papers

367

Zoran Jakšić, Momčilo Milinović, Danijela Randjelović: Nanotechnological Enhancement of Infrared Detectors by Plasmon Resonance in Transparent Conductive Oxide Nanoparticles

376

Branko Livada, Radomir Janković, Nebojša Nikolić: AFV Vetronics: Displays Design Criteria

386

Milenko Andrić, Boban Bondžulić, Bojan Zrnić, Aleksandar Kari, Goran Dikić: Acoustic Experimental Data Analysis of Moving Targets Echoes Observed by Doppler Radars

394

Momčilo Milinović, Damir Jerković, Olivera Jeremić, Mitar Kovač: Experimental and Simulation Testing of Flight Spin Stability for Small Caliber Cannon Projectile

403

Slobodan Jaramaz, Dejan Micković, Predrag Elek, Dragana Jaramaz, Dušan Micković: A Model for Shaped Charge Warhead Design

Martin Macko, Slobodan Ilić, Mirko Jezdimirović: 411 The Influence of Part Dimensions and Tolerance Size to Trigger Characteristics

416

Jure Bernetič, Tomaž Vuherer, Matjaž Marčetič, Mladen Vuruna: Experimental Research on New Grade of Steel Protective Material for the Light Armored Vehicles

422

Hajro Ismar, Zijah Burzic, Nenad J. Kapor, Tugomir Kokelj: Experimental Investigation of High-Strength Structural Steel Welds

Journal of Mechanical Engineering - Strojniški vestnik

Contents

6 year 2012 volume 58 no.